fontstash improvements from other forks

[raptor]

Hi,

I have used a previous fork of font-stash from here:
https://github.com/akrinke/Font-Stash/

I used it at the time because it added two useful features we needed (taken from the readme):

• Added ability to load an arbitrary number of fonts (not just four)
• Use multiple OpenGL textures for glyph caching (not just one)

However, now we need the graphics layer abstraction that you have added to the original fontstash because of changes in the rendering code we have planned in our game (Bitfighter.)

Does the current iteration supports the two features above? And if not, would they be worthwhile to integrate?

Thanks!

[Adam Yaxley]

Absolutely love this library, but this issue really is a blocker making it impossible to know which fontstash is the right one to use. @memononen any chance you could find time for this?