New brains, mushrooms and three-slot system

- New brains: A more standard RNN, trimmed down to optimize both running speed and evolution speed.
- New focus "search" system for Pixlings, which enables them to find things like "nearby enemy with the lowest hp".
- Stamina: Moving drains stamina, but they can rest to regain stamina.
- Removed: Entity memories, pheromones, buckets, speaking and old attention mechanism.
- Fortify buff: Stacks up to 10 times and add one armor per instance. Damage = baseDamage / armor.
- Mushrooms: Health/mana/stamina/fortify mushrooms that the Pixlings can eat to restore some of their corresponding value. These also give Pixlings more of a reason to roam the world.
- Heal ability.
- Stun ability renamed to Boomerang.
- Three-slot system: Eyes, arms and legs now each have a list of abilities to choose from. For instance you can have Eyes: Laser, Arms: Boomerang and Legs: Stomp. The selected abilities evolve over time.
- Auto-pause game on extinction events.
- Removed drowning and made Pixlings that enter water teleport to some other part of the island instead. This is to encourage exploration (vs. just going in circles).