def each_tile level
			size = tile_size level
			(0...size).each do |y|
				(0...size).each do |x|
					yield(x, y) if block_given?
				end
			end
		end
def each_tile level
			size = tile_size level
			(0...size).each do |y|
				(0...size).each do |x|
					yield(x, y) if block_given?
				end
			end
		end
Builds the "x, y" pairs, and returns these pairs in block