Add some short options to CLI

[chiroptical]

It seems like elm-format should have some short options for users on the command line. The most obvious candidates are --yes and --output. It would be interesting to hear arguments for other short arguments from the community.

I built and test this on Linux, via

stack setup
stack install shake
stack runhaskell Shakefile.hs -- build
stack runhaskell Shakefile.hs -- test