Switch the arguments to cowboy_req:stream_body/2

Make them consistent with the rest of the module.
No need for fully qualified call to the same module
Shorten the parse_header clauses
Parse the x-forwarded-for header as a list of tokens
Remove cowboy_req:peer_addr/1

This kind of function is highly dependent on the proxy used,
therefore parsing was added for x-forwarded-for instead and we
just let users write the function that works for them. The code
can be easily extracted if anyone was using the function.
Remove process_post, post_is_create, create_path, created_path callbacks

Instead it will always go through content_types_accepted and it is
up to the resource code to do any creation and to return the created
path if the method is POST and the client should be redirected to the
created resource's location.

This removes the meta value 'put_path' as it is not needed anymore.

This fixes an issue with PATCH where content types were not normalized.
Don't accept TRACE or CONNECT methods by default in REST

For the simple reason that the REST code does nothing about
them.
First draft of the REST chapter in the guide