Pooled curb client using common_pool lib to prevent "Curl::Err::MultiBadEasyHandle" when using in a multithreaded environment.

* Uses https://github.com/jugend/common-pool to allow for high-performance HTTP requests for a multi-threaded environment.
* Properly handles `Curl::Err::MultiBadEasyHandle`
* I will write tests if you think there's validity in this PR.