Base Writer class used by most subclasses of Ext.data.proxy.Server. This class is responsible for taking a
set of Ext.data.Operation objects and a Ext.data.Request object and modifying that request based on
For example a Ext.data.writer.Json would format the Operations and their Ext.data.Model instances based on
the config options passed to the JsonWriter's constructor.
Writers are not needed for any kind of local storage - whether via a Web Storage
proxy (see localStorage and sessionStorage) or just in memory via a MemoryProxy.