helper function that takes a start and end index and returns a slice of all indexes inbetween (inclusive).

PART is for when you're only talking about specific lines that have been modified.

UNSELECTED is for when the commit file has not been added to the patch in any way.

WHOLE is for when you want to add the whole diff of a file to the patch, including e.g.

PatchBuilder manages the building of a patch for a commit to be applied to another commit (or the working tree, or removed from the current commit).