Add lexer for Janet

[sevvie]

All I did was copy the clojure.lua file over, change the appropriate parts of the file, and added janet to the filetype.lua core plugin because I needed it; I figured others might want it too.

[mcepl]

Lexers are fetched from upstream: https://github.com/orbitalquark/scintillua/. You should open the PR there.

[sevvie]

https://github.com/orbitalquark/scintillua/pull/66

I've taken the lexer out of this PR and moved it to a PR on scintillua.

[jgarte]

Lexers are fetched from upstream: https://github.com/orbitalquark/scintillua/. You should open the PR there.

How are lexers fetched from upstream? Is a script used or just manually?

[mcepl]

Lexers are fetched from upstream: https://github.com/orbitalquark/scintillua/. You should open the PR there.

How are lexers fetched from upstream? Is a script used or just manually?

It's actually more complicated than that. The problem is that vis actually supports only old deprecated API for scintillua.

• Currently there is unfinished branch scintillua with the updates, but it has been last touched in 2021 and it doesn’t currently apply cleanly on the top of the current master branch and it doesn’t contain the current version of scintillua API (yes, I tried).
• Martanne’s reaction to the new API was not enthusiastic (to say it mildly), but later in the ticket he seemed to give in.
• There is current fresh PR to refresh API #1018, which I need to investigate.

It's a mess.