Add stdin support

[Andrew15-5]

I'm using Neovim with sbdchd/neoformat and it nicely works with formatters that support stdin (all of them). But typst-fmt doesn't support stdin. It already can output to a different or the same file, but it also should be able to just purge formatted file content to stdout. So, something like a --stdin flag/option would be a great feature. It will get data from stdin and output it to stdout unless output option is present.

[Andrew15-5]

I found how to use non-stdin-compatible formatters:

let g:neoformat_typst_typstfmt = {
  \ 'exe': 'typst-fmt',
  \ 'replace': 1,
  \ }
let g:neoformat_enabled_typst = ['typstfmt']

[astrale-sharp]

Great idea!

[astrale-sharp]

It's on the work on the bin branch

[astrale-sharp]

added!