Add enum and flags member methods

Add all methods from GIEnumInfo to both enums and flags classes.

https://bugzilla.gnome.org/show_bug.cgi?id=693099
overrides: Remove Pango.Context.get_metrics

Remove the override for Pango.Context and the get_metrics method. This can
be done now that tail end method arguments with "allow-none" are implicitly
defaulted to use None/NULL.
overrides: Remove Gtk overrides with tail end allow-none keywords

Remove overrides for Widget.render_icon, TextIter.begins_tag, ends_tag,
toggles_tag, and TreeModel.filter_new. These overrides added an
optional keyword=None for allow-none arguments. This is now implicitly
accepted by the PyGObject machinery so the overrides can go away.
overrides: Remove GLib.Source.attach

Remove GLib.Source.attach override now that tail end allow-none arguments
default to None when not specified.
docs: Fix array length argument skipping with preceding out arguments

Remove split_function_info_args and use a list of all arguments for
generating skipped index lists. Determine argument skipping based on the
full argument list in each in/inout and out/inout argument list buildouts.
This fixes a problem where out arguments preceding array length arguments
would still show array length arguments in the docstring. This was due to an
index mismatch when using split lists instead of list of all arguments.
overrides: Fix __repr__ for various Gdk structs

Change __repr__ overrides for Gdk.Color, Gdk.RGBA, and Gdk.Atom to return a
string reprentation that is valid Python given an expected environment.
See: http://docs.python.org/2/reference/datamodel.html#object.__repr__