Maintenance release, no new features

* Docs updated
* `atty` crate dependency removed

Windows: default file extension is `.md`

Recent versions of `notepad` can deal with `.md` files. From this release on,
all created note files on all platforms have `.md` extension.

Configuration file: the variables `app_args.*` interpret
`{{ get_env(name="<ENVIRONMENT_VARIABLE>") }}` as templates variable.

Maintenance release: improve the natural language detection speed

Maintenance release:

* Improve the natural language detection speed
* Reduce the binary size by 20%
* Improve the test harnesses

Add compilation feature `lang-detection`

Rename the root dir marker `.tpnoteroot`; Add pseudo lang. tag `+all`

* Breaking change: rename root directory marker file from `.tpnoteroot` to
  `.tpnote.toml`.

* Allow optional project specific configuration data in `.tpnote.toml`.
  Tp-Note will source the configuration for all note file in all subdirectories.
  Empty `.tpnote.toml` content is still allowed.

* Interpret the pseudo language tag `+all` in the environment variable
  `TPNOTE_LANG_DETECTION` and the configuration file variable
  `tmpl.filter_get_lang` as "select all available languages".

Maintenance release

To improve the template readability the following template filters have
been renamed:

* `ext` to `file_ext`
* `stem` to `file_stem`
* `tag` to `file_sort_tag`
* `trim_tag` to `trim_file_sort_tag`
* `copy_counter` to `file_copy_counter`

The new environment variable `TPNOTE_EXTENSION_DEFAULT` allows setting the
file extension of new note files. If set, it overwrites the
`filename.extension_default` configuration file variable.

Link docs with new sort-tag shorthand link syntax:

*   Hyperlinks to other Tp-Note documents can now be shortened by referencing
    only the target's sort-tag, e.g. `[my doc](<home/20230510-my note.md>)` is
    equivalent to `[my doc](<home/20230510>)`. Autolinks can be shortened as
    well: `<http:home/20230510-my note.md>` becomes `<http:home/20230510>`

*   New environment variable: `TPNOTE_CONFIG`

*   The prepend_dot filter is replaced by the prepend filter.
    The concerned filename templates have been updated.

Add `TPNOTE_EDITOR_CONSOLE` and `TPNOTE_LANG_DETECTION` environment variables

Doc: Update documentation; Tmpl: add opt. filter parameter

The filter `map_lang` can now be parametrized with a default value that
is returned when the filter input is the empty string:
`map_lang(default="foo")`.

This includes: `tpnote_lib` v0.18.2

Feature: add natural language detection

Regression fix of the viewer feature (under Window only)

This commit fixes some bugs introduced since v1.19.1. These regressions
only appear when compiling for Windows:

* Fix 70b615f: "Bug fix: path method not appropriate for URLs"
  (bug introduced in commit 97d2be7)
* Erroneous path handling when compiling for Windows:
  - The `.is_absolute()` path method acts differently under Windows.
    Fix in: c648342
  - Under Windows the `std::path::Component`s `Prefix()` and `RoodDir`
    need special care. Fixes in: 632e31a and 3ea8de2
  - Rust's Windows Paths optionally have `\` as path separator:
    Fix in: 0b61979

As mentioned above, these fixes only concern the proper function of
the viewer when compiled for Windows. None of the bugs have security
implications.  Nevertheless, I decided to yank the whole v1.19 series
because for a good user experience the viewer is expected to work.

Reduce C library dependencies.

This crate replaces two crate dependencies. This allows
the hassle free crosscompilation of the targets:
`x86_64-unknown-linux-musl`, `armv7-unknown-linux-gnueabihf` and
`x86_64-pc-windows-gnu` on Debian.

Add env. var. `TPNOTE_BROWSER`, `TPNOTE_EDITOR`

Braking changes:

* Env. var. renamed from `TPNOTELANG` to `TPNOTE_LANG`
* Env. var. renamed from `TPNOTEUSER` to `TPNOTE_USER`

Viewer: better detect changes with simple editors

In theory watching only `file` is enough. Unfortunately some file
editors do not modify files directly. They first rename the existing
file on disk and then  create a new file with the same filename. As
a workaround, we watch the whole directory where the file resides.
False positives, there could be other changes in this directory
which are not related to `file`, are detected, as we only trigger
the rendition to HTML when `debounced_event.path` corresponds to our
watched file.

Viewer: bugfix: highlight indented source code

Fallback to plain text for unkown prog. language

Make highlighting configurable

Improve syntax highlighting,

remove GPL3.0 licensed dependency.

Capitalize `{{username}}`, fix: `tel:` is not local

Export HTML: add abs. link base marker `.tpnoteroot`