Include FORECasT predictions

[jmerkin]

Hi. This looks like a very useful package. I was wondering if you might add predictions from the FORECasT tool from Leopold Parts' group to predict frame-altering edits from Cas9. The repo is available here: https://github.com/felicityallen/SelfTarget.

[Jfortin1]

Great idea, we'll add it to the list of new features to implement