And update user-font text_to_glyphs() method to match.
Currently disable the win32-font text_to_glyphs(), until that one
is updated. Or better yet, remove it and implement ucs4_to_index().
It's the toy font API afterall.
The init func does not actually need to draw anything, but having a cairo_t
similar to that passed to render_glyph is handy for computing font extents.
This is because cairo makes doing some things really hard (if not impossible)
without a cairo_t.
The user-font-proxy test case is a great example of how the added cairo_t
makes life much easier.
