ConnState is only provided for reading from: do not return it
Include an accessor module for the #websocket_req{}

websocket_req.erl was created by a pair of fairly trivial substitutions
on the list of fields in the record def of #websocket_req{}. This should
be automated per-build (with dynarec?)
Make websocket_req() an opaque type
Merge pull request #1 from sanmiguel/jc-dialyzer-warnigs

Pass the internal state to the behaviour's callbacks as a websocket_req() to better match what Cowboy does with websocket.
Fix outdated naming of ConnState to WSReq
Merge branch 'jc-dialyzer-warnigs' of github.com:jcomellas/websocket_client into jc-dialyzer-warnigs