webserver: add URL router with support for <vars>
webserver: drop d_that
webserver: bundle all request data into class HttpRequest

Now, pathArgs could actually be used by handlers.
webserver: first batch of new API URLs

Note that return data is still in old format.
Import Aki Tuomi's yahttp
link in yahttp
switch to yahttp in auth

A bit more intrusive than needed, but now everybody has a HttpResponse
object.
Switch pdns-recursor webserver to common HTTP infra

Session and Server learned to use mplexer.
Writing the response is still a hack, so is the listening address.
add webserver= &co settings to recursor