Add an .editorconfig file, to describe how code should be indented

[mavit]

This matches what perltidy is configured to do, where applicable.

Many text editors support being configured with this. https://editorconfig.org/

[oalders]

Can we pare this down to only the filetypes present in the repo and not automatically generated?

The Makefile and META.json files are automatically generated, so we don't want anything to try to re-format it.

There's no HTML either. 😄

[oalders]

Thanks, @mavit!