Log Message:
Update to version 0.3.1.

Changes:
 * added -t option to normalizer so that only messages with a specified
   tag will be output
 * bugfix: abort if a tag was assigned to a message without any fields
   parsed out (uncommon scenario)
 * bugfix: mem leak on parse tree destruct - associated tags were not deleted
 * bugfix: potential abort in normalizer due to misadressing in debug
   message generation