d2format: Expose in CLI under fmt subcommand

[nhooyr]

• ci/dev.sh: Add
• lib/xmain: Print usage info in separate log
• d2format: Expose in CLI under fmt subcommand

[scsmithr]

I have a small request on this. Would it be possible to allow providing the input on stdin? I'd like to get formatting integrated into my emacs setup and it's easier to do that with tools that accept file contents on stdin.

[pleshevskiy]

@scsmithr Yes echo "h1;h2;h3;" | d2 fmt -

I've already added PR to the neoformat vim plugin sbdchd/neoformat#438

[scsmithr]

Oh nice, then this works for me.