fix up staircase room positioning
so that staircase is not adjacent to room's corner
move BlockCell methods in PathFinder
change blocked cell character in comment cause 'x' is clearer than '+'
move CellIsBlocked method in PathFinder
fix spelling error
change direct uses of kInfinity weight to CellIsBlocked calls
remove returning by value of struct type cause it can be assigned to
add actual saving of room information inside dungeon level
fix initial staircase digging
change down staircase generation
to position them out of cells adjacent to room's corners
add blocking of adjacent cells for up staircases before room digging
to not generate staircases inside rooms
remove blocking of adjacent up staircase cells in DigUpStaircases method
 cause they are already blocked
fix possible infinite loop in down staircase generation
change down staircase generation
so that down staircase has 5 solid adjacent cells just as up staircases have