combined line-oriented and regular diff mode

[ajs124]

Not sure how viable this is or how interested you are in implementing something like this, but I think neither the line-oriented nor the regular diff mode are optimal, but rather a combination of the two.

Basically, I'd like a diff view like the one github or gitlab (and probably a bunch of other things) offer.

An example from a PR, set to unified instead of split diff mode, looks like this:

[Gabriella439]

@ajs124: I'd accept a pull request for this, but I'm unlikely to implement this myself

[Gabriella439]

You might be interested in: #38