Added support for post requests

[FredericOccedat]

Added a post function able to POST some requests (with the same throttling abilities as the existing GET), with the possibility to pass data in the request too.

For simple post request without data, a request should look like: "http://my-server/my-path/1234"
For post requests with data, a request should look like: {:url "http://my-server/my-path/1234" :form-params {:param1 "value1" :param2 "value@"}}