Glitches!

First stab at it. My code is not as ugly as I was worried it would be! Please tell me if it's too ugly tho.

Also, this doesn't actually do anything unless it's called, so I suggest something along the lines of this in `map.lua` for POC purposes.

```lua
-- Here is a little bit of hacky code to create a glitches object and
-- modify the map. How do we actually want to do this?
require("glitches")
local glitches = Glitches()
glitches.load_layer(tile_layer)
glitches.generate_glitches(20)
glitches.modify_layer()
```