added __getitem__ to Maps to retrieve a spaxel or a map
added __getitem__ to Maps to retrieve a spaxel or a map

sdss/marvin,bretthandrews/marvin,albireox/marvin,sdss/marvin,bretthandrews/marvin,albireox/marvin,albireox/marvin,albireox/marvin,sdss/marvin,bretthandrews/marvin,bretthandrews/marvin,sdss/marvin