🚀 Add config to control vertical spacing

[iandunn]

I'd like to be able to change the amount of vertical space around elements. For example:

• Increase the space between a filename and the last hunk from the previous file
• Decrease the space between a filename and the first hunk in that file

I couldn't find anything in the existing config that would let me change that.

[dandavison]

Does this PR give you what you want? #2028

[iandunn]

I think so, thanks!