gplugin/gplugin

Migrate to gi-docgen

2021-08-30, Gary Kramlich
f402012569a8
Migrate to gi-docgen

gi-docgen is apparently the future and it works much faster with no extra work like updating `gplugin-docs.xml` that gtk-doc required.

However, there are a few additional python dependencies for gi-docgen, notably `python3-jinja2`, `python3-pygments`, `python3-toml`, `python3-typogrify`. I'm in the process of updating the builders right now as the docs build by default now.

Testing Done:
Ran locally and via the new convey plan.

Reviewed at https://reviews.imfreedom.org/r/905/
# Dependencies
GPlugin depends on the following at a bare minimum:
* glib-2.0 >= 2.40.0
* gobject-introspection, libgirepository1.0-dev
* meson >= 0.42.0
* gettext
* help2man
* a C compiler
A full build (enabled by default) depends on the following:
* gtk-3
* python3-dev, python-gi-dev, python3-gi
* libperl-dev, libglib-perl, libglib-object-introspection-perl
* liblua5.1-0-dev, lua-lgi
* valac
All of these packages and their development headers need to be installed
prior to building GPlugin.
# Building
GPlugin uses [meson](https://mesonbuild.com/) as its build system. As such
compiling is a little bit different than your typical `./configure`, `make`,
`sudo make install`.
Meson requires you to build in a separate directory than your source. As such,
these instructions use a separate build directory.
To compile you need to run the following commands:
```
meson build
cd build
ninja install
```
If you want/need to tweak the build system (to enable/disable certain loaders)
you can do so at any time by using `meson configure` in the build directory.