Major Breaking Change: Simplify Codebase using Http-Primitives Lib and Remove Streams

[andrewlalis]

This will be a major version increment, which will break pretty much all tests, unit and integration, and will break pretty much all current usages of handy-http. I'm doing it though, because I think that it'll be better in the long run for handy-http to be more cohesive and less tightly coupled.

Essentially, the high-level description of the changes is this:

• I'm introducing a new library, http-primitives that defines primitive HTTP types like HttpRequest, HttpResponse, HttpRequestHandler, etc. in a generic way using only plain D and the standard library.
• I'm refactoring handy-http to remove its own implementations of the types that http-primitives provides. (In actuality, I cut and pasted modules from handy-http to http-primitives with minor tweaks here and there.)
• As a result of the refactoring, handy-http's role will be reduced to being an HttpServer compatible with any request handler defined using http-primitives. Think of it as being inspired by Java's servlets, where you can write a servlet using the Servlets API, and then pop it into any servlet container implementation you want (tomcat, jetty, undertow, ...). http-primitives serves as the cross-project API, and handy-http becomes a (default) server implementation for that API.

What this means:

• The signatures for many functions will change.
• Most all documentation will need to be updated. I'll see about finding a more modern documentation generator thing while I'm at it.
• I'm removing usage of my streams library, and going back to using plain D ranges, to improve compatibility with everything else.

[andrewlalis]

Closing this for now, since reducing to ranges seems to have some pretty dire consequences for how to handle low-level IO for both HTTP and websockets. May revisit in a completely refactored handy-http project in the future...