Add a rate limited request filter

[mgreene]

Purpose

While having the ThrottledRequestFilter providing a concurrency limit and implicit back pressure into the caller, another gauge would be helpful in fine tuning request speed. I've added the ability to specify the number of requests per second in addition to the number of concurrent requests allowed at any given time.

Implementation Decisions

• I've utilized Guava's RateLimiter to do most of the work
• With regard to the maxWait argument found in the ThrottledRequestFilter, I decided to keep with that theme. Given that both the semaphore and the rate limiter perform a tryAcquire(), I've decided to split the maxWait across both of those operations. So if you provide a maxWait of 1000 ms, the algorithm will reduce any ms spent in the semaphore acquisition and pass that reduced amount into the rate limiter's tryAcquire.
• I've bumped the Guava version to 14.x, I did not notice any class loading issues in my testing.

[slandelle]

Oh man, it looks like you've developed what I've dreamed of for my own project for months!
@jfarcand @rlubke I'll soon be off and won't be able to review and test this before about 2 weeks, so feel free ;)

[jfarcand]

Pretty good work, I've merged it after review. I will take another look later this week, but so far so good!!! More patch like that welcomed!

[mgreene]

@jfarcand Thanks, happy to help :). Any idea when this will make its way into maven central?

[rodrigoalvesvieira]

This is amazing. Thanks!