💥 Mines

Finally, a new gameplay element, mines! They destroy walls, trigger nearby mines and blocks, and they deal exactly one damage to nearby players and enemies. And they can throw players a bit.

Now there are some mines scattered throughout the published levels, to open passages, and as a player hazard.

I decided to cheat by preventing enemies from triggering the mines on contact, down in the hit-resolution code. The intelligent-enemy-mine-avoidance code was going too slowly - it needs more design. The red shooter enemies will still accidentally shoot mines though, and I kept that for now.

Other changes:

• I added a wall outline. I always wanted to do that.
• Now it's possible to hide powerups, and mines, under the yellow blocks. :-)