Tower climb 20k maps

[kywch]

I used tower climb to test sweep on percentile score, where the difference between 99% and 99.9% matter.

Summary of changes

• Unified the map format to bitmap, which was already being used internally. Generating and loading the maps were slow, but these were also made faster.
• Generated and saved 20k maps, which contain way harder maps than before (max moves increased to 30 from 15).
• Updated hyperparams based on sweep
• Made LSTM work in the new 4.0 interface, with minimal changes I hope. We should revisit this later.