GitLab

Test plan:
- repeat aarch64 function CI job; observe whether success rate improvement

This ensures the installed manpages always match the installed version,
and simplifies the release process. An optional dependency on `help2man`
is added (default on, can be avoided with `-DENABLE_MAN=OFF`).

Since the autotools build system is deprecated, manpages are simply
removed from the autotools build.

Manpages are intended to be used on Unix-like platforms. Therefore, the
build instructions for Windows include `-DENABLE_MAN=OFF`, and in Gitian
manpages are now excluded from the Windows releases (zip file and
installer).

This also fixes a bug in the Gitian build where it would unnecessarily
extract the source tarball without using the extracted stuff.

Test plan:

* `./autogen.sh;./configure --enable-deprecated-build-system;make
install`
* `cmake -GNinja . -DENABLE_MAN=OFF;ninja install`
* `cmake -GNinja . -DENABLE_MAN=ON;ninja install;man bitcoind`
* Gitian builds for all platforms (verify hashes, inspect
Linux/MacOS/Windows zip files, try Windows i...

This moves auto-generation of Markdown documentation out of
`contrib/devtools/gen-manpages.sh` and into the build system, with a new
ninja target `doc-md`. `contrib/devtools/gen-manpages.sh` returns to its
original purpose of generating manpages only (can be integrated into the
build system later as well).

The auto-generated Markdown documentation is no longer committed into
the repository, but built as needed. CI will build it for GitLab pages,
so that docs.bitcoincashnode.org will always be fully up-to-date with
the master branch. A `DOC_ONLINE` option has been added to the build
system to differentiate between documentation generated for the website
and for local use (default off), replacing the previous CI hacks.

Test plan: `ninja doc-html` (with `-DDOC_ONLINE=ON` and
`-DDOC_ONLINE=OFF`),
https://bigblockiftrue.gitlab.io/bitcoin-cash-node/

Long-term purpose of this MR is to allow shipping offline HTML
documentation along with our releases, so you can always locally access
HTML docs for your specific installed version (online documentation is
only for latest version). This is a lot more user-friendly than manually
browsing an unorganised bunch of Markdown files.

Simplified logic of which files to include for `mkdocs`: everything in
the `docs` folder plus any `.md` files outside it. This dramatically
reduces the run-time of `mkdocs` and the size of the generated
documentation folder. It also broke links to source code files. These
links can be removed in a follow-up MR.

Additionally:

* Changed site directory from `site` (default) to `doc-html`.
* Renamed `files-for-mkdocs` directory to `doc-html-src`.
* Moved `mkdocs.yml` into `doc` folder.

This also makes the following changes for locally building
documentation, but these changes are reversed when building online
documentati...

Reduces ccache to max 3GB, from default of 5GB. Uses the CI extend
functionality to create build directory and print ccache stats, rather
than repeating these steps for every job.

This adds debug builds (CMAKE_BUILD_DYPE=Debug) for GCC and Clang on
Debian.

Note: I went through the changelog between RFC 7159 and RFC 8259
(included within RFC 8259), and found nothing that affects us.

Cross-compile for aarch64 and run test with emulator

Follow-up of !571

This coverage checks the RPC functions. The CI will complain if any RPC
methods are not tested.

This creates a job that runs the full extended suite of tests, instead
of the setup we have now here quick tests and long tests run in two
separate jobs. This is required to be able to test full coverage.

This re-enables the search bar and makes the header logo link to docs
homepage regardless of deployment location.

Test plan: https://bigblockiftrue.gitlab.io/bitcoin-cash-node/

Get rid of some dead links in documentation, both removing entirely dead links, and updated links that needed it.
This should make links work correctly both in GitLab and on docs.bitcoincashnode.org.

One link (to src/.clang-format) could not be handled by `mkdocs` - probably it has issues with dotfiles.
This link has been turned into a non-link.

Additionally, temporary folders created by the `mkdocs` deployment have been added to .gitignore:

- `files-for-mkdocs/`
- `site/`

Test plan
---------

You will need the `mkdocs` program installed to test this - see gitlab-ci.yml's `before_script` section of the `pages` job for relevant commands.

- On a checkout of this MR, manually perform the commands in the `script` section of the `pages` job in `.gitlab-ci.yml`.
- Check that no warnings or errors are reported by the `mkdocs build` command
- Run 'mkdocs serve' and inspect the documents at https://127.0.0.1:8000
- Check that relative links work in GitLab's folder view of the documentation

As discussed in !451 this creates a new folder containing all that is needed from the entire source tree, and run `mkdocs` on that folder.

Changes contained here:
* build site from entire tree, allowing access to documents in various other directories
* adjust `mkdocs.yml` to point to correct folder for all docs
* the above fixes a lot (most) of broken links
* exclude most of `src` and `depends`, include only those files from there which are linked
* fix up bare URL links, make them into markdown links
* a few doc reference improvements (e.g. to `doc/README.md`)

This increases the built site size from 33M to 41M, remaining under current limit of 100M.

Test plan:

* run the doc deployment CI steps in `.gitlab-ci.yml` manually to create the folder and build the docs using `mkdocs`, checking only that it builds.
  Note: there will still be some broken links, these will be fixed in other MRs.
* use `mkdocs serve` to inspect the docs

This publishes our contribution and disclosure policies on the projects
documentation website.

The 'phonon' network upgrade has activated.

GitLab's 'only/except' syntax is considered deprecated.
While it is not strictly clear to me whether we need to move to the new
rules: syntax ahead of 22 May 2020, we are proactively doing so.

New CI jobs should be specified using rules: syntax where needed.

Test plan:
- review
- check CI pipelines are functioning correctly
  (compare prior to this change)

Reference:
https://about.gitlab.com/releases/2020/05/06/gitlab-com-13-0-breaking-changes/

This generates and deploys the documentation in the doc/ folder to
gitlab pages on each update of the master branch.

Explicitly adding needs allows them to start in parallel with static
checks.

Previous behaviour was to wait for previous pipeline stage (static checks).

Ensure building with unix makefiles does not regress again.

Includes ABC -> BitcoinCashNode renamings.

The created binary has changed name in the `ninja` build, and that's inconsistent. This MR reverts the binary's name back to bench_bitcoin, while leaving the current ninja targets as-is.

TEST PLAN:

A. Checkout and build, check that the file built has the expected name; check the ninja targets in master and in this MR

1. The before and after behaviour of `ninja bitcoin-bench` does not change: it will build the benchmarking binary
2. The before and after behaviour of `ninja bench-bitcoin` does non change: it will build and run the benchmarking binary
3. The name of the binary has changed from `bitcoin-bench` to `bench_bitcoin`
4. A new ninja target exists `ninja bench_bitcoin` which actually builds the `bench_bitcoin` binary; the `ninja bitcoin-bench` target is only an alias to this one.

B. Check the latest pipeline for the MR.

Adds jobs to test that we can build the software using clang. Also runs
unit tests built with clang.

Runs the `bench-bitcoin` target using ninja.
There are no artifacts generated at this point.

Test plan:

- verify that `test-debian-benchmarks` job is successfully executed
  in CI pipeline

This jobs will run the longer running tests only.

These jobs only run on the `master` branch.

see https://docs.gitlab.com/ee/ci/junit_test_reports.html

This change adds 3 new targets: Win64, ARM and "no wallet".

The cross-platform targets need a dependency compilation stage. "No
wallet" also gets a unittest target.

All jobs are set to have explicit dependencies, so all tasks that can be
run in parallel, do run in parallel, regardless of stage.

This splits the CI process into 3 stages and multiple jobs.

It also adds a new base image with all the dependencies pre-installed.

Stage "build" build the main project.

Stage "build_test" builds the tests. This was separated out to avoid the
build stage taking more than 1 hour on cold cache.

Stage "test" spawns four jobs and runs unit tests and functional tests
in pre-upgrade and post-upgrade states.