Added tinyxml2 header and source files.

tinyxml2 will be used for reading in some game data in the XML format,
particularly the tile maps for the game world.
Removed tinyxml files and installed separately.
Updated license year(s) to 2012-2013.
Added basic class declarations for tile maps.
Added missing documentation and updated the rest.
Merge branch 'tile_map'

Conflicts:
	.gitignore
	Makefile
	tile_map.hpp