Minimum mask size has been increased

I've added code to all the relevant collision functions to now do tile checks on the middle of the mask as well as the corners, which means you can now have masks up to 2 times the tile size (TS).  Check the read_me to see which functions were updated, but all moving platform and collision functions will cater for the new mask sizes.  This small gif shows the mask can now be twice the size of the moving tile below it.