Ability to run in checking mode

[Kernald]

It would be nice to be able to run textpbfmt on files in CI to check that they're properly formatted. google-java-format exposes this use-case through two options for example:

  --dry-run, -n
    Prints the paths of the files whose contents would change if the formatter were run normally.
  --set-exit-if-changed
    Return exit code 1 if there are any formatting changes.

[kssilveira]

hi, I agree.

One workaround would be to write the output to a different file and then do a diff.