Filesystem Heirarchy Standard (FHS) paths

If no instance directory specified, then use paths like
/etc/serval/serval.conf
/var/cache/serval
/var/log/serval
/var/run/serval
etc. for files, instead of all in a single directory.

Log all directory creation as INFO messages.

Interpretation of log.file.directory_path has changed slightly.

Updated servald configuration tech doc.