Add styling to autodoc content

Add colors, formatting and font to autodoc generated content, that
mostly is suffixed by ".sig-".

Signed-off-by: Jorge Marques <jorge.marques@analog.com>

Remove walrus operator to support Python >= 3.7

Signed-off-by: Jorge Marques <jorge.marques@analog.com>

Theme customization, author mode code quality

Allow to include light/dark logo with light_logo and dark_logo theme
configuration variables.
Add dark_css_variables and light_css_variables to allow docs to inject
dark/light variant CSS specific rules.
Improve author mode code quality.

Signed-off-by: Jorge Marques <jorge.marques@analog.com>

Add interref role, a in-org alt to intersphinx

Interref role suffixes the ref role with the format ref-<repo> (e.g.
ref-hdl) to create cross references between different docs inside the
org.

Currently, the tracked repos are manually set on lut.py, with plans to
automate or self-service the inclusion of new repositories.

For versioning handling and multiple hosted, the environment variables
are used:
* ADOC_INTERREF_URI: set the host uri, can be a link or local.
* ADOC_INTERREF_TAG: enable tag suffix, e.g. pyadi-iio/main.
* ADOC_INTERREF_RELEASE: enable release tag suffix, e.g. pyadi-iio/v1.0.0

Signed-off-by: Jorge Marques <jorge.marques@analog.com>

Fix popen, repo case, simpler author-mode just gen

Fixup process open not waiting it finish.
Consider capitalization in repository names (e.g. no-OS).
Allow author-mode -g flag without directory.

Signed-off-by: Jorge Marques <jorge.marques@analog.com>

Regression fix, improve doc

On 4e1ae98 the `i` character was accidentally included to the find method,
breaking the behaviour of the git role.
Also, move doc info and add npm note to the README.md.

Signed-off-by: Jorge Marques <jorge.marques@analog.com>

Deploy doc on last stage, pull request ci

Upload build-doc artifact to be downloaded on the last stage, avoiding a
failed run to write the gh-pages page.
Also, add a pull-request workflow, which is the same as the main.yml but
stopping on the middle-stage.

Signed-off-by: Jorge Marques <jorge.marques@analog.com>