RFE: add support for namespace ID record types

[rgbriggs]

Add support for namespace identifier record types. There will need to be new auxiliary record types for namespace identifiers for existence, add, delete and set/change events.

Currently the set appears to be: AUDIT_NS_{INFO,{INIT,DEL,SET}_{MNT,UTS,IPC,USER,PID,NET,CGRP}}

See: https://github.com/linux-audit/audit-kernel/issues/32