implement cookies support within `net\http\Request` and add tests to demonstrate
ensure `Content-Length` header is set for all POST and PUT requests, even when body length is zero.
allow for multiple headers with the same key when parsing a response message (i.e. Set-Cookie)
implement cookies support within `net\http\Response` and add tests to demonstrate
implement `\action\Request::headers()` and `\action\Request::to('string')` to behave as expected in correlation with their counterparts in `\net\http\Request`
simplify `\action\Response::render()` and header output; move shorthand header magic to overloaded `header()`
Merge pull request #902 from pixelcog/request-response-cookies

Improve Li3 Request/Response Classes