This method allows you to handle arbitrary HTTP method types, mapping
them to callables. Typically, these will be methods of the controller
instance: e.g., array($this, 'foobar'). The typical place to register
these is in your constructor.
Additionally, as this map is checked prior to testing the standard HTTP
methods, this is a way to override what methods will handle the standard
HTTP methods. However, if you do this, you will have to retrieve the
identifier and any request content manually.
Callbacks will be passed the current MvcEvent instance.
To retrieve the identifier, you can use "$id =
$this->getIdentifier($routeMatch, $request)",
passing the appropriate objects.
To retrieve the body content data, use "$data = $this->processBodyContent($request)";
that method will return a string, array, or, in the case of JSON, an object.