Every plugin is now accesible in a separate repository

Conflicts:
	Makefile
	config.c
	config.h
	document.c
	ft/djvu/Makefile
	ft/pdf-mupdf/Makefile
	ft/pdf-poppler/Makefile
	render.c
	zathura.c

The command definitions are now updated to fit to the updated
definitions of girara.

* We don't fail if we can't load a plugin. There can be anything.
* Reintroduce the command line parser from glib.
* Use fstatat as it is more reliable than d_type from dirent.