add support for multiple request modes

From getting close to rolling this into production, it was discovered that certain socket conditions can cause the https calls to the canvas API endpoints to be sporadic. Like 80% of the calls randomly not going through. Sadly after a day of debugging, curl calls work flawlessly by drupal socket based ones don't. So we should provide a way of selecting the method of making calls. drupal_http_request or httprl_request or a flavor of curl_init baked in.