Webhooks: support additional methods (PUT, DELETE)

There are many integrations out there and many of them now expect that people can call REST endpoints with the proper method.

As an example, we have an integration right now where we can POST to create a person in another system, which returns an ID. Ideally, we would like to PUT to the user record to do an update. This is currently not supported by Marketo, the only options are GET and POST. A few old timey servers out there support ?_method=DELETE or ?_method=POST on the URL of a POST, however that number is very few.

Please add additional methods to webhooks so we can take advantage of additional, modern integrations.