Add an interface for Reinforcement Learning.

Implement a simple HTTP server to start games, receive the gamestate and
pass commands to the simulation.
This is mainly intended for training reinforcement learning agents in 0
AD. As such, a python client and a small example are included.

This option can be enabled using the -rl-interface flag.

Patch by: irishninja
Reviewed By: wraitii, Itms
Fixes #5548

Differential Revision: https://code.wildfiregames.com/D2199
This was SVN commit r23917.

binaries/system/readme.txt

@@ -42,6 +42,9 @@ Examples:
 3) Observe the PetraBot on a triggerscript map:
  -autostart="random/jebel_barkal" -autostart-seed=-1 -autostart-players=2 -autostart-civ=1:athen -autostart-civ=2:brit -autostart-ai=1:petra -autostart-ai=2:petra -autostart-player=-1
 
+RL client:
+-rl-interface       Run the RL interface (see source/tools/rlclient)
+
 Configuration:
 -conf=KEY:VALUE     set a config value
 -nosound            disable audio