Add ninja file generator

[schmir]

Sorry to bother you one last time.

I've played around with the ninja build system a bit and in lacking another project to try this on, I've implemented a ninja file generator for rolling-shutter.

This solves some of the problems the current approach with the Makefile and the bb.edn file have.

Usage is like build.clj; ninja or build.clj -x.

It's written in clojure, so you may prefer to rewrite it in python or not use it at all :)