Feature Request: Throttle

[thejeff77]

With large enough files and enough languages, this spams the API past its limit resulting in timeouts and reset connections.

To scale well, I recommend supporting bulk translations - x at a time.

Second, if requests are throttled to one at a time, or have a pool with a maximum number of executors would help keep requests constant over time, rather than scaling up rapidly to handle all input at once.

[thejeff77]

Thanks for the invite. Looks like throttling wouldn't be too bad - the async library you use has a queue function if you search "### queue(worker, [concurrency])" on v1.5 https://github.com/caolan/async/blob/v1.5.2/README.md

[thejeff77]

#7