Parse sfl4j log messages

This module parses sfl4j log messages into the following fields:

- Severity (integer)
- Timestamp (table created by "date_time")
- Class (string)
- Message (string)
- Stacktrace (string)

It wraps up long stacktraces as a single string joined by "\n".

I plan to submit a decoder to Heka for dealing with these messages.
stackline will match this first (so basically it will never match anything)