add a leading slash to #hackney_url{path}

It seems to be an oversight that #hackney_url{path} doesn't start with a slash, and also that hackney will send the url fragment when making a request.

Some web sites, like stackoverflow for example, will not like that request.


This patch adds a leading slash to #hackney_url{path}
and sends #hackney_url{path} instead of raw_path in the request function