net/http.Handler

This change makes `falcore.Server` a proper `net/http.Handler`.  This should allow for greater compatibility with other `net/http` based applications as well as provide support for Google App Engine.

The key compromise here is we had to privatize the `Request.Connection` property.  Since it can't be acquired in these new use cases, we don't want anyone to rely on its existence outside of the library.  I think this is probably for the best since it's undefined what would happen if a third party modified the connection.

We should, in the future, expose something like `net/http.Hijacker` for more advanced use cases.  Though, this would make it awful tricky to support spdy transparently...