Rework how special arguments are marshalled

Introduce an array of param_types for special arguments (callbacks,
arrays with explicit length). This means that now more than one
callback is supported for each function, and you don't need to
specify an explicit length for arrays.

https://bugzilla.gnome.org/show_bug.cgi?id=646632

Conflicts:

	test/js/testGIMarshalling.js