Extended robot.brain to act as a general-purpose key-value store.

Additions:
 - robot.brain.set
   For storing arbitrary key, value pairs under a private namespace to avoid collisions.
 - robot.brain.ger
   For getting from store by key.

Signed-off-by: Diwank Singh Tomer <diwank.singh@gmail.com>
Merge branch 'extended-brain'