Spin off extensions

[michaelklishin]

Some Jig components are quite opinionated or not very easy to understand (e.g. cljs-builder). I suggest that they are moved into their own repos at some point. This may complicate some things but will make it easier to use Jig itself in my opinion.

[malcolmsparks]

Thanks. Actually that's always been my intention. The cljs-builder has a legacy from working the same way as Pedestal, I'll rewrite it soon to work the same way as lein-cljsbuild.