Formatting a directory into other directory about elm-format

[avh4]

I think we should leave this out for v1. I'm expecting the most common case to be that people run elm-format on their whole project to update everything in-place. --output would be for a) people just testing out the tool for the first time or that need to do one-off formatting, and b) people who are writing scripts or other tools. I don't think formatting one directory into another would be that helpful in either case, since (a) should have version control, and (b) will probably be iterating files themselves.

[avh4]

If anyone has had a need for this in a real project, please comment below.