mmrfc5424addhmac milestone: actual hash function integrated
mmrfc5424addhmac milestone: add capability to configure digest to use
mmrfc5424addhmac milestone: do not process non-rfc5424 messages
consistently use new message protocol type #define's
expose so-far msg-internal method to query structured data

This also lead to a slight performance optimization in the msg.c
module (when it comes to querying structured data).

This is stage work in order to provide the capability to fully
parse structured data.
milestone: mmpstrucdata parses STRUCTURED-DATA (but does not yet store it)
milestone: mmpstrucdata persists to json tree

but not yet to a specific subtree
mmpstrucdata: add structured data in explicit subtree
mmrfc5424addhmac milestone: detect if "our" SD-ID is already present

... and stop processing in this case (as required)
simplify STRUCTURED-DATA representation in msg object
mmrfc5424addhmac: complete initial implementation

hash is now also persisted back to structured-data rsyslog
property
remove no-longer needed data item
Merge branch 'v7-stable'
Merge branch 'v7-stable-mmrfc5424addhmac'

Conflicts:
	Makefile.am
	configure.ac
	runtime/msg.c
	runtime/rsyslog.h