alias `cowboy_req` to `Request`

I think this adds more clarity to the code.
Improve reading the request body
Update documentation for `read_body`
Update function name change in the change log.
Merge pull request #44 from scrogson/replace_deprecated_function_calls

Update request body reading for cowboy 0.10.0
Change the parser api to use read_body options
Update to Elixir v0.14.0