Add bitmap string rendering

[profexorgeek]

Most 2D game engines support bitmap font strings using fonts generated by a program such as AngelCode BMFont. Frostflake currently can't draw strings.

Spiritually, the UI in FrostFlake should probably be handled by the DOM and the glut of robust UI frameworks available for the web. However, there are many cases where strings should render directly in the engine and FrostFlake needs some pattern. JavaScript can directly draw strings to the canvas but not with custom bitmap fonts like games often use.