Add new themes

[mccarthy-m-g]

Four new themes!

earth

"earth" is like an inverted version of the forest theme (similar to how "sky" is an inversion of "water" or "plum" an inversion of "violet").

paper

"paper" is a purely black and white theme. There's obviously overlap with the "grayscale" theme, but I think this still has its own appeal with its starker contrast.

magma

"magma" is a dark theme inspired by the LCARS computers from Star Trek, which I also have a custom code chunk highlighting theme to go along with if we ever add that to Apero. Doubles as a Halloween theme... 👻

primer

"primer" is a dark theme that uses the colour scheme from GitHub's dark primer theme.

Asides based on my experience making these

• It might be nice to add documentation on how to contribute new themes, if that's something we're interested in. It's easy but we could make it easier 😄
• Some more options on the colours of specific elements in the theme might be nice. For example, having footer and icon link colours be their own thing rather than tying them into the $navLinkColorCustom option. So adding: $footerLinkColorCustom and $iconLinkColorCustom as options.

[apreshill]

These are awesome, thank you for contributing!

[mccarthy-m-g]

Thank you, and you're welcome!