Cleanup comments, move mapdata stubs out of the loops they were in, fix default region id
optionsdata class to allow adding string option values during json init. Also add "DEFAULT_REGION"
  option.
* executed via optionsdata.add_value("OPTION_NAME", "value", "optional value txt");
* handles de-clobbering values that are not builtin, if the value is added later
  ( the game loads options (and sets default for invalid options) before data_init)
overmap: support DEFAULT_REGION option for new overmaps, and save/load the region
  settings id so players can choose another region for the next overmap, and there
  isn't a magical game-wide transformation of forests into deserts or such.