Documented the scenes module.
Documented the torterra module.
Fixed the log module's documentation to match doxygen's format.
Moved the screen overlap checking function to Camera (previously Surface::is_on_screen()).
Added screen overlapping checks in the Surface-derived classes.
Changed the way Tileset returns Tile objects.
Removed unneeded typedefs.
Modified the way Map stored its tiles, using Tileset's use of share_ptr for Tile objects.