added hex_grid_t::for_each_chunk() which takes a takes a function and calls it with each chunk added hex_grid_t::num_chunks() util func to make things slightly easier
added hex_grid_t::for_each_chunk() which takes a takes a function and calls it with each chunk
added hex_grid_t::num_chunks() util func to make things slightly easier

mflagel/asdf_multiplat,mflagel/asdf_multiplat,mflagel/asdf_multiplat