Added an option to stop at splitter

[mikkelking]

Thanks for writing the medium article and contributing this package, it has saved me some considerable work.

In the test data I assembled, I used emails from our system, and discovered that the some links in the code are wrapped by the email system. and planer detects them as normal lines, and therefore includes the whole email instead of just the reply text.

I made a change to add an option to ignore these false positives and only take the response up to the splitter.

I also introduced some debug statements, thanks to the excellent npm debug module https://github.com/visionmedia/debug. To activate debugging output, prefix your command with DEBUG=planer