* middleware/proxy: give Exchange a context
Make context.Context the first paramater in the Exchange method.
This is inline with all other query functions.
* up the version
* middleware/proxy: absorb httpproxy
Move the httproxy into proxy. This adds and Exchanger interface which
is used to exchange the messages with the upstream.
The https_google upstream will re-resolve itself and update the upstream
hosts used every 300s.
* Remove and add TODO
