Add a way to load TTF fonts as outlines.

[SiegeLord]

There's an existing patch here, seems like a good idea:

https://www.allegro.cc/forums/thread/611384

[EdgarReynaldo]

I will take a look at this. I will try to "update" the patch to match current master branch first, and then I will see if it needs any modifications. One major concern I have is whether a single font should render a glyph or an outline or both. I can see the need for having an outline alone, with no body to the characters. That could be cool for lighting effects. They should always be saved with white though, so we can pass a color to al_draw_text_etc...and have it render the border that color on demand through a tinting blender.