Add smart-shift-mode recipe

Hi, 

This recipe provide a minor mode `smart-shift-mode` for shifting line/region to the left/right by infer the current major mode indentation level.

I build this package for the [PR](https://github.com/bbatsov/prelude/pull/552) to the `prelude`.

Repo is here: https://github.com/hbin/smart-shift

Thanks