Exposed things necessary to translate HTTP <--> CoAP

At the moment to translate between CoAP and HTTP seems to require hosting a HTTP server using CoAP.NET. However in my application I already have a server with HTTP requests coming in, this change allows me to internally translate those requests into CoAP requests and send them on to the appropriate CoAP device, and then translate back to HTTP for the response.

Signed-off-by: Martin Evans <martindevans@gmail.com>