implemented support for Tiled (www.mapeditor.org) tileset offset feature (https://github.com/bjorn/tiled/issues/16). The offset is now available as a CCTMXTilesetInfo property, and CCTMXLayer instances use it to set the anchor point of tile sprites
Merge remote-tracking branch 'tompave/tileset_offsets' into develop-v2
updates AUTHOR and CHANGELOG