Chart-review

This release adds a `Kappa` field to the `accuracy` command's generated scores.

This is [Cohen's Kappa](https://en.wikipedia.org/wiki/Cohen's_kappa), which might be useful in addition to the F1 score.

Initial release!

The only current command is `chart-review accuracy` which will calculate F1 scores, a confusion matrix, and some other stats between two annotators.