[Cogl] [RFC] Separate out CoglPath api into sub-library

[Robert Bragg]

I've made a patch to split out the CoglPath api into a cogl-path
sub-library like cogl-pango and cogl-gst which would be good to have
some review for, but since the patch is rather large I've just pushed
it to a wip/split-cogl-path branch instead of sending directly to the
mailinglist.

For reference I've copied the commit message for the patch below.

kind regards,
- Robert

--

Separate out CoglPath api into sub-library

This splits out the cogl_path_ api into a separate cogl-path sub-library
like cogl-pango and cogl-gst. This enables developers to build Cogl with
this sub-library disabled if they don't need it which can be useful when
its important to keep the size of an application and its dependencies
down to a minimum.

There were a few places in core cogl and cogl-gst that referenced the
CoglPath api and these have been decoupled by using the CoglPrimitive
api instead. In the case of cogl_framebuffer_push_path_clip() the core
clip stack no longer accepts path clips directly but it's now possible
to get a CoglPrimitive for the fill of a path and so the implementation
of cogl_framebuffer_push_path_clip() now lives in cogl-path and works as
a shim that first gets a CoglPrimitive and uses
cogl_framebuffer_push_primitive_clip instead.

We may want to consider renaming cogl_framebuffer_push_path_clip to
put it in the cogl_path_ namespace.