Issue #263 LogfileInput parsing improvements

- Fix the file handle leak in file discovery
- Update the journal to store the location and length of the last record
  (not backwards compatible, existing journal files will fail to load and a new one created)
- Add the regexp parser
- Keep the token parser since there are some performance benefits (10-15%)
over the regexp parser (mainly do to the final conversion from byte array to string)
- Remove the Logline struct and use a pipeline pack instead. This is cleanup and
preparation for the protobuf parser which needs access to the pack and message)
Merge pull request #391 from mozilla-services/issue_263

Issue #263 LogfileInput parsing improvements