Refactor PLN files with PEP-8 formatting

I refactored the PLN files so that they would be compliant with PEP-8 formatting guidelines. I wanted to make them more consistent and easier to work on as more people will be using them.

Most of the changes were to line length, whitespace and docstrings. I didn't touch the camel-cased names, though.

I also added a bunch of comments throughout the code where there were some questions about existing functionality.

Note that I have not altered any of the actual PLN functionality in this pull request.

(fyi @jadeoneill)