logsig: add pseudocodish C skeleton for signature algo
add test/PoC logsigner tool
logsigner: sign via merkle tree approach (still PoC, non production)
logsig: PoC for some TLV support functions

also first steps at integrating them into rest of PoC
logsig: build base plumbing for signature multi-provider interface
Add imjournal module for reading messages from systemd journal.

For reading messages with all fields from structured systemd journal
log messages.
Loading module with $ModLoad imjournal is enough to start pulling messages
no other configuration is needed.

	modified:   Makefile.am
	modified:   configure.ac
	new file:   plugins/imjournal/Makefile.am
	new file:   plugins/imjournal/imjournal.c
	new file:   plugins/imjournal/imjournal.h
configure.ac fix

	modified:   configure.ac
Add all fields from journal message (including non standard).

	modified:   plugins/imjournal/imjournal.c
Ignore systemd journal internal messages (without facility)

	modified:   plugins/imjournal/imjournal.c
Added internal log info when message from journal doesn't have MESSAGE

	modified:   plugins/imjournal/imjournal.c
logsig: more interface plumbing
logsig: first PoC of actually writing to signature file
logsig: write block-sig record

also some general improvements, e.g. random data is now gathered
correctly
logsig: add support to read signature files

... still incomplete ...
logsig: preserve necessary state during file closed time
logsig: add config parameters (for omfile)
logsig: implement sig.block.sizelimit parameter
logsig: write integers in most compact from to tlv file
logsig: update hash chain algorithm to match updated paper
logsig: update implementation to new concatenation rules from paper

- when concatenting hashes, the hash ID must be included
  (actually the imprint, not just the hash is concatenated)
- when concatenting integers, the smallest number of octets
  must be used (actually, we have just level currently, which
  always is one octet)