Nerd Fonts, True color support

[kins-dev]

So based on the open pull requests, you're probably not maintaining this anymore, but I figured I'd do the right thing anyways.

This adds:

• True color support with graceful fall back to 256 colors and 16 colors (uses nearest-color for fallback)
• Nerd Fonts Caskaydia Cove as that works well for Microsoft Terminal/VTE/Kitty
• Handles to the custom text
• Wide screen support (700 px was just constraining, now that's a minimum and a max of 90% of the screen space)
• Scrolling in the prompt elements area when there are a lot of elements
• Better color management overall
• Use of \033 instead of \e as some versions of bash handle \e badly