Add a new section under "Additional writings" section about how
BuildStream integrates with Docker. At present, this section includes
only two sections:

- "Run BuildStream inside Docker", that refers to existing instructions
for doing so
- "Generate Docker images", that adds instructions for using the newly
added `contrib/bst-docker-import` script

In future, this document can be extended to include the following
things:

- Importing Docker sources via `docker` source plugin - if/when the
Docker source plguin is moved from bst-external to BuildStream proper
- A Docker sandbox, if/when that is added

As suggested in
!857 (comment 106809743),
add a NEWS entry for `contrib/bst-docker-import` that was added
recently.

Add documentation and NEWS entry about bst-docker-import

See merge request !864

README: Update to add link to website

See merge request !859

This will be the place to store low level data types used
throughout the core, for now this includes public and private
types.

And slightly touch up the doc strings for Consistency and Scope.

Refactor types api

See merge request !870

Jonathan Maw authored Sep 14, 2018 and Lachlan committed Oct 11, 2018

This is benign because a _yaml.ChainMap doesn't raise a
KeyError, but it's not required to be a ChainMap.

Jonathan Maw authored Aug 22, 2018 and Lachlan committed Oct 11, 2018

Note that the ProvenanceFile's names will be incorrect after loading
from the cache, but this is currently only used for writeback, which
isn't used in junctions.

* Fix to CWD issue provided by Jonathan Maw

Jonathan Maw authored Oct 08, 2018 and Lachlan committed Oct 11, 2018

Previously, key calculation had to be done manually, creating
unnecessary boilerplate. This has now been subsumed into YamlCache.get
and YamlCache.put (Yamlcache._get and Yamlcache._put_from_key exist for
old behaviour).

YamlCache.write is now private.

Private methods have been put at the end of the class.