feat(docusaurus): Add syntax highlighting for Tact and FunC

[novusnota]

Closes #11

I also took the liberty of changing the highlighting of the dark theme to One Dark, because the Tact Docs and Nujan IDE use it. And also because it doesn't utilize the same colours for different entities as often as the current one here (Dracula).

Still looks a bit noisy, but colors can be adjusted furthermore if needed. I'd make variable capture look white there, perhaps (see this and this for a "how-to"):

[jubnzv]

Thank you!