Support for multi-line events.

Pull request for Ticket #108.

Add support for multi-line event.

Line are merge if the match one regular expression:

* multiline_regex_after: If a line match this regular expression, it will be merged with next line
* multiline_regex_before: If a line match this regular expression, it will be merged with previous line

If both regex are undefined (which is the default) normal behaviour of line per line is used.