Cleans up code and adds default response data

- remove trailing whitespace
- default response data for status-only Response(Int) and Response(Int, String)
- various syntax changes for clarity
Adds Httplib and decouples Websockets, Http, et al

- Changes the request and client handling API to use new functions
  `handle` and `is_websocket_handshake` that dispatch on the handler.
- Http exposes a WebsocketInterface abstract type with default
  implementations of these functions that throw errors.
- Websockets implements these for a WebsocketHandler, which it defines.
- In addition, generic stuff like Request, Response, Headers, et al.
  have been moved to an Httplib module.
Fixes broken openSSL regexp