4.0.0

So this library went through a bit of churny phase, my apologies for that. It was caused by a couple of factors; moving the library to a new home, a new rendering engine and me trying to abstract said rendering engine for reuse in metalsmith-layouts.

However, the end result is now a stable plugin, that's easy to use and easy to maintain. Jstransformers are way simpler to debug, and so far I haven't even encountered any bugs. We're not abstracting the rendering engine because it's just not worth it, and confusing apis have been removed. All in all I hope that you'll enjoy this release and feel free to let me know if you encounter anything!

• breaking: dropped node 4 support
• breaking: the filename property is no longer set automatically, use https://github.com/MoOx/metalsmith-filenames
• removed metalsmith-engine-jstransformer for ease of maintenance