gplugin/gplugin

Silence warnings from Python files

2021-09-29, Elliott Sales de Andrade
4a32fb36235b
Silence warnings from Python files

The `Python.h` header must be included first to appease the preprocessor.
Additionally, it includes ``, ``, ``, ``,
`` and ``, so we don't have to.

Also:

* Mark Python code as `ssize_t` clean
We don't use any `#` format variants, but it's best to define this for any future usage.

* Remove unused struct members from Python loader

* Simplify `gplugin_python3_filename_to_module`
I believe the call to `g_utf8_strrchr` was in error, as the second argument is
length in bytes, but `g_utf8_strlen` returns length in characters, which is
shorter. In any case, it accepts -1 anyway, so there's no need to count the
length.

Testing Done:
Compile and `ninja test`

Reviewed at https://reviews.imfreedom.org/r/960/
# 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.