Add rainbow-delimiters module

[jamesoff]

Adds support for rainbow-delimiters, which replaces tsrainbow2.

I'm marking this as draft as I've not been able to successfully make docgen due to the following, which I don't know enough about the moving parts to fix:

nightfox.nvim % make docgen
Error running Lua:
misc/panvimdoc/scripts/panvimdoc.lua:198: attempt to perform arithmetic on a nil value (field 'incrementheadinglevelby')
stack traceback:
        while rendering Pandoc
stack traceback:
make: *** [docgen] Error 84

(I just did brew install pandoc to install it, hopefully that's correct.)

If you can handle that part, this is hopefully good to go.

[olssonks]

I found that if you add the line --metadata="incrementheadinglevelby:0" \ to the MakeFile, this fixes the problem with running docgen.

I don't know why this isn't an issue for others. It seems usage.md hasn't been changed by any of the PRs after the rewrite(#77), where panvimdoc was added to .gitignore. Maybe other folks just aren't running make docgen, so they haven't encountered this problem.

.PHONY : docgen
docgen: $(pandocdir)
	@pandoc \
		--metadata=project:nightfox \
		--metadata="description:A highly customizable theme for vim and neovim" \
		--metadata="incrementheadinglevelby:0" \
		--lua-filter misc/panvimdoc/scripts/skip-blocks.lua \
		--lua-filter misc/panvimdoc/scripts/include-files.lua \
		-t misc/panvimdoc/scripts/panvimdoc.lua \
		usage.md \
		-o doc/nightfox.txt