Adding FTGL sources to the external directory.

This will allow us to modify the ftgl sources so that we can
render to opengl vertex and index buffers.
It will also allow us to extend the PackedShape to UnpackedShape
paradigm.  With freetype-gl text unpacking and determining the bounding box
of the text could only be done in an opengl context, due to the way it
always try to load to the gpu whenever a glyph is retrieved.
With ftgl we can keep the PackedShape and UnpackedShape paradigm.
We can upack without having to wait for an opengl context.