Implement Memory Q-networks

[Kaixhin]

Control of Memory, Active Perception, and Action in Minecraft introduces a memory Q-network (MQN) and recurrent MQN (RMQN), based on a relatively simple key-value soft attention memory. These could feasibly be added as model options, although the feedback RMQN (FRMQN) would add another level of complexity to the architecture.

Edit 2016-06-14: DeepMind have been working on something similar. Expect to see something from them in the future.