Load variables from json & yaml

adds a `-d` flag to `bin/tilt` which loads json or yaml into variables.

Also adds [ronn-format(7)](https://rtomayko.github.io/ronn/ronn-format.7) documentation and a `rake man` task to generate from it.

This adds no automated testing, and may have missed some changes to the `gemspec`. It also might make sense to add man page help ala [`bundle help`](https://github.com/bundler/bundler/blob/0bf058c8643dbd2bebce60142db64146aaf31331/lib/bundler/cli.rb#L40)