Multiple transform support

I've got a [collection of transforms](https://github.com/tivac/mithril-codemods) that don't really make sense to be run individually. I'd like to provide a straightforward way to run them all against a group of files. I don't see a way to do this with `jscodeshift` currently, but it seems useful.

[`ava-codemods`](https://github.com/avajs/ava-codemods/blob/f8637ec80c25be2032421fdea2ab5dcd363ab7df/cli.js#L23-L29) does this by running `jscodeshift` once per transform. It's a bit brute-force, but it'll work for now until (if?) `jscodeshift` adds support.