0.24 HTTPClient to allow a request queue limit

This release adds extra constructors so you can specify the request queue limit (see PR #32 ).

This can help facilitate fail fast when a back end service is over-occupied and prevent excessive queuing which likely will timeout anyways.

By default the queue is still unbounded, as that has the potential for the most performance. It is also recommended to never set the queue size to be less than the maximum concurrent requests.