As we have switched from Phabricator to GitLab, we now point at GitLab
documentation on how to automatically link and close issues from
commit messages.

Improvements on the section about commit messages are thrown in for good
measure.

Related to #4732

Related to swh/meta#4960

It is no longer included in the doc toc.

Remove the reference to phabricator

There are plenty of other phabricator links in another places in the
doc, but this ones are the first encountered by a new comer.

Related to swh/devel/swh-docs#4732

Suggested by @zack: “it's useful to have it on top (because a lot people
use docs.s.o for that, at least now), but it also belongs to devel doc,
so people will look for it on the left as well”

After merging various parts of Software Heritage documentation in a
single Sphinx instance, the navigation using the Read The Docs theme
became seriously cumbersome.

We switch to PyData Sphinx theme: a clean, Bootstrap-based Sphinx theme
by and for the PyData community. For details, please refer to:
https://pydata-sphinx-theme.readthedocs.io/

One major upside is that by default supports three level of navigation:

- top-level parts in the header bar (for us, they would refer to
  `devel`, `sysadm` and `user`)
- a left sidebar for sections in the current part,
- a right sidebar for the contents of the current page.

This maps really well to our hierarchy.

Some changes made to better navigate the various parts of our
navigation:

- Rename “Development Documentation” to just “Development”.
- Rename “Sysadmin Documentation” to just “Infrastructure”.
- Rename “User Documentation” to just “Usage”.
- Promote the API reference from Development to the top-level.

Some other improvements to better benefit the new theme:

- Replace the vertical logo with the horizontal one to better fit the
  header.
- Add links to GitLab, PyPI and status.s.o to the header.
- Remove the unused Alegreya font.

vlorentz authored 2 years ago and vlorentz committed 2 years ago

The only two titles at the second level were 'Important documentation links'
and 'Content', which look weird and are not very useful.

And this level prevented headings inside package documentation from being
shown in the TOC at all, which means the TOC couldn't be used to navigate
within a package's documentation.

These changes allow to build all SWH documentations (developmment, system
administration and user) using a single sphinx-build command, meaning they
are now merged into a single one with shared index of references.

Development documentation is now rooted to docs/devel, user one to docs/user
and sysadmin one to docs/sysadm so a good amount of files were moved.

A couple of configuration files and makefiles were updated to reflect that change
and the building / cleaning processes were made more reliable.

Calling make in root directory of swh-docs will execute the development build
of the documentation in a tox environment while calling make in docs folder
will use the current virtualenv.

It remains possible to build each documentation in a standalone way by
calling make in their root directory.

Closes #4496