* Separated out rivers and bridges into its own file with three map variants
* fixing tags
* removed extra 4 starting positions from the medium map since it only supports 8 players
* update GetUnoccupiedPoints to consider hazards with a flag
* use new utility method to fine unoccupied points and enforce map sizes
* changed up casting to make IsAllowable() more usable
* fix for rivers and bridges snake start positions
* update max player count, add unit test
* set player count to 12 (max for smallest size)
* fix: one of the 19x19 spawn points
* randomize snake placement at start positions
* randomly choose starts in quadrants
* fix: check that start positions are valid
* modify food placement to avoid hazards