def each_collidable(&blk)
			@width.times do |i|
				@height.times do |j|
					cell = get_cell(i, j)
					if cell != 0
						blk.call(i, j)
					end
				end
			end
		end
def each_collidable(&blk)
			@width.times do |i|
				@height.times do |j|
					cell = get_cell(i, j)
					if cell != 0
						blk.call(i, j)
					end
				end
			end
		end
calls a block for every cell that is not 0.
 params: col, row