Highlight Support

[Jothsa]

This should work. All the tests pass. A few things I'm not sure about:

• The user can customize the highlight query param name, but it has to be set in both the PagefindUI script and PagefindHIghlight script. This is kind of annoying, but I don't see another way.
• I have provided optional styles, but they're so minimal that I don't know if it's worth it. They're basically the browser default styles. Maybe it would be better to use some of the --pagefind css vars?

I'll try to add docs later Added some docs

[bglw]

Amazing, thank you for putting this work in!

I have a bit of a busy week/weekend, but I'll crack into reviewing this next week ❤️

[bglw]

Sorry to leave you hanging! Had to deal with some tasks that were put aside while working on the 1.0 release. Coming back around to new PRs and issues in this repo soon.

[bglw]

Apologies again for the delay — implementation looks good! I'll make a few docs tweaks before the next release, but I can tackle that after merge.

Thanks for the contribution! ❤️

[bglw]

Finally got this out the door in 1.0.4 🙂 Made a few changes, you'll see some notes in #502

Thanks again!