HTTP client: prepare new API:
 1. Allow configure useragent, timeout per request
 2. Remove proxy support
 3. Combine ITextHandler & IBinaryHandler into one => IResponseHandler. Clojure is dynamic
 4. HttpClient.exec the only level API, remove .get .post => they could be better implemented in Clojure
HTTP client: new Clojure API
Merge pull request #5 from ptaoussanis/master

New async & sync HTTP client API