analysis across multiple runs of pairs/students that show up most frequently

[benedictbrown]

This probably has to be a separate script that parses a collection of index.html files produced by compare50. But it helps detect patterns of students overcollaborating across many psets.

[cmlsharp]

To my knowledge, this is planned for the eventual compare50 webapp which won't be stateless like the command-line tool is, but a command-line script would definitely be useful in the meantime.