Add support for promotions using LinkedIn-style linked itemized lists

[ftrifoglio]

Desired result

[CLAassistant]

All committers have signed the CLA.

[thehale]

Hi @ftrifoglio thanks so much for this PR!

I've been working on a similar feature internally and will definitely use some of your ideas too.

[ftrifoglio]

@thehale After some further tinkering I noticed that my implementation breaks if a a multi-experience block spans across multiple pages. I think that's because tikzpicture edges don’t automatically carry over to the next page. But haven't looked into this yet.

[thehale]

The latest version of Expressive Resume now has a "parser-friendly" design for promotions, largely inspired by your work here (though the final implementation looks very different).

While I'm closing this PR instead of merging, I did list you as a co-author on 7d3c416d9a76b11697af9aebe8e3c2e2d6b25aef to credit your contribution.

Thanks so much!