Rebase Commits, sorry but it needed to be
Fix the load of external Tileset
Merge remote-tracking branch 'upstream/master'

Also corrected a typo: "dimension" doesn’t make sense, it must
be "dimensions".

Conflicts:
	lib/tiled_tmx/map.rb
	lib/tiled_tmx/tilelayer.rb
	lib/tiled_tmx/tileset.rb