Scott Batson

Allow user to pass cached locations to `generate`

1

## What's in this PR? If you want to get percentages from a CFI, you have to first `generate` the locations. This can take a while, especially if the book...

## What's in this PR? Fixes https://github.com/futurepress/epub.js/issues/1311 The types listed for `currentLocation()` on `rendition` were incorrect. The function returns a `Location`, which has a `start` and `end` of `DisplayedLocation`