grim/gplugin

Make doc/introspection options yield to parent.
develop
2020-08-22, Elliott Sales de Andrade
71e98ba93d21
Make doc/introspection options yield to parent.

This allows `meson -Ddoc=false` to automatically propagate from Pidgin to the gplugin subproject, without having to specify `-Dgplugin:doc=false`.

Reviewed at https://reviews.imfreedom.org/r/87/
There are a few notes about building on OSX.
First off, building has *ONLY* been tested against homebrew. If you want to
support fink or macports, please let me know and I will merge your pull
request.
Currently there is no known way to build the Perl loader on MacOS. So you
**MUST** run meson with `-Dperl=false`.
## Lua
For the Lua loader to work, you need to install `lgi` from luarocks either
systemwide or to a virtual environment created by LuaDist, vert, or something
along those lines, then you just need to run `luarocks install lgi`.
## Python
If you're using homebrew, you need to install `pygobject3`.