Feature/json resource

Make it possible to fo a GET that returns handler info as JSON. It is conceptually similar to the debug request in that it does not make a subsequent upstream call. The motivation is that an application can make a call to the deviceproxy service outside the request-response loop.
The conversion is a safeguard against handlers returning non-string elements as headers. You could arge that a handler that does not do that is broken, but my JSON response handler counts on that to do its job. Everything is centered around headers and I piggy back on it to slip in JSON objects as the values, hence the need for my unicode() conversion. The architecture allows me no other opportunity.

I can't assume ASCII. Would an isinstance(value, types.StringType) check suffice?