Diff highlight should also show emphasis on deleted code

[hugo-vrijswijk]

The new diff highlight is spectacular ✨✨✨, but I'd like it to be closer to a 'real' git diff by not only showing extra highlight on the replacement text, but also on the replaced text.

See:

Compare this to other diff tools which also highlight the old code:

[nicojs]

Sure, go right ahead 😁