Slow During Startup

[BodneyC]

Hi,

I love the colorscheme but when I started using it I noticed a lag when opening vim (nvim in my case but it seems to do the same with both).

I assumed this was because the <SID>set_hi function was being called for every group despite repeated color definitions. I forked the repo and hi linked all the repeated groups which took 1989's startup time effect from ~22ms (my slowest plugin) to ~9ms.

I didn't want to make a PR because the resulting code is arguably less readable/maintainable and might not be what you want for the repo.

Just after your thoughts on performance here.