[PATCH] v1: Logging cleanup and systemd journal support

[Torsten Hilbrich]

This series of patches is based on the "Logging and --help
updates" series posted by Aleksander Morgado
<aleksander at aleksander.es>.

It start with cleaning up some parts of the logging code. The the
existing logging support (supporting syslog and file-based
logging) is split into two different functions using a function
pointer to select them. Then the support for logging using the
systemd journal is added.

[PATCH 1/5] log: Refactor evaluation of log level
[PATCH 2/5] log: Refactor log level text output
[PATCH 3/5] log: Add mapping from glib loglevel to syslog priority
[PATCH 4/5] log: Introduce function pointer to handle different log
[PATCH 5/5] log: Add support for journal logging