Multiple tilesets, autoloading of images and image object (when gid is assigned)

[stvoidmain]

I have a working version of this nice library with multiple tilesets, autoloading of set image (even when external) and also autoloading of images for objects when one is used, letme know if you're interested and i can make a patch or pull request.

[ibilon]

That would be of great help yes, thank you.

[stvoidmain]

Just posted a pull request wich include some parsing fixes and this.