FEATURE REQUEST: Support linting multiple dashboards

[dineshdh]

Request to support linting multiple dashboards by providing a directory path instead of a filename. This could be based on a -d flag or merely checking if the provided arg is a directory or not.

The code should loop through all the .json files in the directory and lint them. Perhaps based on a -r flag this could support linting files recursively as well, picking up and .lint files along the way.

[marians]

I second this request!

Regarding recursion into sub-directories, I would expect this as a default behaviour.