Provides a generic rate limiter for node.js. Useful for API clients, web crawling, or other tasks that need to be throttled. Two classes are exposed, RateLimiter and TokenBucket. TokenBucket provides a lower level interface to rate limiting with a configurable burst rate and drip rate. RateLimiter sits on top of the token bucket and adds a restriction on the maximum number of tokens that can be removed each interval to comply with common API restrictions like "150 requests per hour maximum". A synchronous method, tryRemoveTokens(), is available in both RateLimiter and TokenBucket. This will return immediately with a boolean value indicating if the token removal was successful.