font: add unfinished freetype backend

font: add unfinished freetype backend

This is a first attempt of a freetype2 backend for the font drawing functions.
This avoids the heavy pango/cairo dependencies, although, we might lose
important font handling that pango does for us like correctly drawing combined
characters.

This is still a stub implementation. The drawing operations are not supported,
yet. Use --enable-pango during configure to enable the still working pango
backend.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>