Coloured Shields

This update adds a reverse walker, colours, and a new passive: shield.

I've tried for some time to make a walker that runs away but the AI just wasn't quite right. Whilst it made for a great ally, it was not so great an enemy. So I settled on a new fleeing method and made it attack when an ally is adjacent.

It's really hard to see what's going on right now. Thus, the enemies are now orange and the allies are teal. I'm still not satisfied with the palette but it's a lot easier to play and make sense of.

Undo means a lot of things that were deemed to cruel in Ending are easy to explore. So 2 hit turner-enemies are out, and a new passive ability called Shield is in. This swallows the first hit an entity takes. Later levels in the endless mode are now ludicrously hard, especially with hooked monsters in the mix. I've halved the rate at which passives are added to make it allow one to get a bit further.

I've also added ally-doors. These are doors that only enemies can open. I've not added any to the endless mode, though I could do so if they were initially protected. I think they will make for some interesting puzzles when I get round to adding more.