Optional Underline and Spell Foreground Colors

[dylnmc]

fixes #106 (now SpellBad et. al. have appropriately colored foreground colors).

Also, this fix allows the user to disable underline with let g:nord_underline = 0. This applies to all underlines globally.

I feel like I might have a go at refactoring nord.vim to be slightly more efficient and concise while retaining all functionality and customization (and potentially adding more where it might be a good idea), but this fix works for now.

Although, it might appear strange to set s:underline = "NONE,", you can test for yourself and see that it works to disable underline without affecting any other term= attributes.

This also is referenced in #105

[arcticicestudio]

Superseded by #127

Thanks for your contribution 👍

Sorry for the delay, I've had no free time (job 👨‍⚕️, study 📖, life 🏋️‍♂️ etc.) to work on my or any other OSS project (see Tweets 🐦 from April and June), but from the beginning of July I finished my studies and can finally spend time on OSS again 💚

Sadly the original repository doesn't exist anymore so I had to pull the changes and create the new PR #127. Your code looks good to me. I've only changed the name of the config from nord_underline_comments to nord_underline (like you also mentioned in the PR description) and added a new section in the documentation.

I'll merge #127 to release the next version as soon as possible.