Docs Productization: Marshalling

Productize content for marshalling and protostream.

Modularize existing content.
Show consistent examples for usage (i.e. should match CLI example).
Identify additional changes and work to develop customer content.

Review Server Guide marshalling section (8. Adding Custom Marshaller Bridges) and make sure this is relevant and up to date for DG 8

From Ryan:

• protostream and marshalling:
  The important things to document are:
  Jboss marshalling no longer present by default, infinispan-jboss-marshalling jar must be added to the classpath of the client/server if required.
• Externalizers ignored unless this is present
  Protostream is the default marshaller for user types. Need to document the process of generating marshallers using pojos, and configuring the serialization context.
• Best practices on how to evolve schemas to ensure backwards-compatibility
  Possible to configure a custom user marshaller in embedded mode, for example if the user wants to use Java Serialization but not jboss marshalling.