For serializing to commit log, and potentially internal wire messaging.
Note: intentionally incompatible with stock C wire/serial format.
Note: intentionally separate from the CQL-centric serialization
for a few reasons.
1.) Need "bulk serializers" for internal objects (mutation etc)
which might not fit well into the "types.hh" serializer schemes.
2.) No need for polymorphism/virtual type parameters since we know
exactly what we serialize and to where.
