option for overriding HTTP-header

[AydinChavez]

Add method parameter to options for overriding the proxy-outgoing HTTP-method.

Simple solution for issue: #1066

Example usage:

var server = http.createServer(function(req, res) {
  // You can define here your custom logic to handle the request
  // and then proxy the request.
  proxy.web(req, res, { target: 'http://127.0.0.1:9200', method: 'GET' });
  console.log("req: " + req);
  console.log("res: " + res);
});

You could also wrap it into a conditional statement like:

if ( req.method == "POST" ) {
   proxy.web ...
}

[jcrugzz]

Ok, this doesn't seem harmful. Will add this to my maintenance branch @AydinChavez. Thanks for the contribution!

[jcrugzz]

superceded by #1251