lsp semantic highlight support

[hexbloom]

Hey there! Thanks for the great theme. I recently upgraded to NeoVim 0.10.0 which has support for semantic highlighting. I noticed that this theme didn't had support for it, so I threw together this commit, see the below image for the result. It's based off of the treesitter highlights but I commented most of them out to be more minimal with the implementation.

Let me know if this looks good or if some of the options should be tweaked!

[hexbloom]

This PR will resolve #2

[xandkar]

@phha Any opinion on merging this?

My nvim+neoclide/coc.nvim+phha/zenburn.nvim setup looks pretty bad after recent updates (frankly not sure if coc, nvim or rust-analyzer is more to blame, I gave-up rollback experiments), but after pointing my Plug to this PR - things are looking better again.

Please at least consider this 🙏

[lukebakken]

For what it's worth, I have forked this repo, applied this patch, and everything works as intended. Thanks @hexbloom!