Added missing proxies namespace.
Improved file sending - added File class. Updated README.
Moved `Request::buildQueryString()` to GETRequest.
Query string parameters in a GETRequest URL are now parsed into fields on setting.
Replaced multiples calls to `curl_setopt()` with a single call to `curl_setopt_array()` where possible.
Address and port can now be optionally specified in the constructor of proxy objects.