Size of map sprite relative to map size and index.html file

Hi,

Fantastic work on this library. Love its very simple API and how it handles the Tiled Map editor. Feel very productive, although I had to figure out this pull request first :-)

My sprite for the map had a different size than the map itself, that caused the code to have issues with drawing it correctly. By taking into account the actual size of the sprite map, not only the number of tiles, it draws correctly.

Also the mapfile.js was missing in the index.html file.

Too bad this framework does not have any documentation, it seems very easy to use, but it is VERY difficult to get going due to lack of documentation.