Bumping guava to latest version.
This was needed in order to utilize their RateLimiter class.
Refactor out AsyncHandlerWrapper into its own class so it can be reused.
Also cleaned up the ThrottleRequestFilter a bit to remove class level members
that were not needed.
New rate limited request filter, which also utilizes the concurrency limiting
found in the ThrottledRequestFilter
Merge pull request #336 from mgreene/master

Add a rate limited request filter