Introduce ASCIITiledMapLoader

[bitbrain]

Depends on #30.

Create a class which loads TiledMap objects from an input stream which provides ASCII characters. These characters can be translated into tiles and objects respectively.

e.g.:

xxxxxxxxx
x a   b x
xxxxxxxxx

where x is a wall texture (collision), whitespace means air (walkable) and a and b are game objects, specified by the loading instructions.