Use multiprocessing.SimpleQueue on SerenityOS again to work around a recent
regression.

Updated the .af file for SerenityOS to avoid duplicating "Games" in the
system menu.

UI improvements:
    - Multiple colors for the grid in hexagonal mode (meh)
    - Automatically set TERM=linux on SerenityOS and macOS terminals to
      get the numpad to work
    - Added some difficulty presets

Squash merge of branch 0.6.36