Complement main paradigms.

PUT can inform that nothing happens.

OPTIONS is required by web-browser embedded JavaScript calls in order to allow
for CORS.

documentation/source/rest.rst

@@ -27,10 +27,12 @@ Success
 ``POST`` requests which perform some other action such as sending a campaign
 will return a ``"200 OK"`` response if successful.
 
-``PUT`` requests will return a ``"200 OK"`` response if the resource is successfully updated.
+``PUT`` requests will return a ``"200 OK"`` response if the resource is successfully updated and ``"204 No Content"`` in case if no modification was applied..
 
 ``DELETE`` requests will return a ``"200 OK"`` response if the resource is successfully deleted.
 
+``OPTIONS`` requests will return ``"200 OK"`` response with allowed method on given url.
+
 Common Error Responses
 ++++++++++++++++++++++