Split `Git.changedLines` by file

[JordanLongstaff]

Git.changedLines returns the total numbers of added/deleted lines for an entire diff and completely obscures the detail of which files the changes belong to. There should be a way to get the stats for a single file.

[Brock-Gibson]

Bumping, would love to see similar APIs to the other danger tools for doing logic on diffs.

[gianluz]

i'll have a look to this

[JordanLongstaff]

This fork has a function called diffForFile that serves this purpose, but it's currently broken. Its brokenness may be related to #320.