Support for HTTP clients

[TwentyPast4]

Going over the available library options, I noticed there's no good pick for having both HTTP and WS in both client and server roles, which were developed to a point where it would be nice to use. I guess boost beast was closest. Websocketpp is great - and written such that I could relatively easily add HTTP client support to it.

That said, this implementation is not perfect and was tailored to my specific use cases, so the PR might include other changes which might not be directly related or desired. I'm opening the PR for the purpose of presenting a working example on how it could be done and to signal the need for such a feature. Feel free to suggest changes in written form or commit form here or the source repo respectively.