Fix signing of requests which contain query parameters in them.

According to the documentation for  Signature Base String [OAuth 1.0a section 9.1.2](http://oauth.net/core/1.0a/#anchor13)
we should use the absolute url when signing the request.

This patch is based on the fmt branch, which go fmt'd the code to make it easier to contribute.

This patch has been tested with OAuth 1.0a requests which has query params.