Added option to specify a custom separator.

You can use this option to split the text by something different than newline characters.

For example this might be helpful for log files which have log messages spawning multiple lines, e.g.

    2014-02-06 15:16:26,364 - INFO - line 1
    line 2
    2014-02-06 15:16:26,365 - DEBUG - single line
    2014-02-06 15:16:27,364 - INFO - single line

Splitting this by regex `INFO` and the separator for the timestamp `\d{4,4}-\d{2,2}-\d{2,2} \d{2,2}:\d{2,2}:\d{2,2}` will result in:

    2014-02-06 15:16:26,364 - INFO - line 1
    line 2
    2014-02-06 15:16:27,364 - INFO - single line