Refactor player commands

This is in preparation for the conversion of player_t.commands from a
GQueue to a GPtrArray

Reformat CMakeLists.txt slightly (make comments consistent, make
everything fit in < 80 columns... where possible)

Temporarily disable range coder to relieve some CPU load
  - It would be better to have this as part of the server configuration,
    retrieved via HTTP, but for now this has to be set manually