log: enhance setting loglevels

Enable logging level settings such as 'log_level=error' to set all
levels to error, or 'log_level=error,ssdp=maxdebug' to override only one
category
log.c: fix setting custom log levels in the form of log_level=info,http=error

The first facility override wasn't set properly but used the generic level. Also print newlines in the debug warn message when setting up log levels
Merge branch '#111-log_level' into features

Conflicts:
	log.c