add http forwarder

[bradstimpson]

added an http forwarder dispatcher - can be configured in the config.json with http://host/test

[thisisaaronland]

Thanks for your PR. A general-purpose "relay to an HTTP endpoint" dispatcher would be useful. I've added some comments and questions.

[thisisaaronland]

Thanks for the first round of updates and apologies for the delay in getting to them. It all looks good but I've flagged a few more "details".

[thisisaaronland]

It looks like http.go and http_test.go are both still using the bespoek HTTPClient rather than a plain-vanilla http.Client{} instance?

[bradstimpson]

@thisisaaronland any suggestions on how to modify this?

[thisisaaronland]

Something like this?

#29 (comment)