Lumberjack 2.0.0-beta4 migration

Updated to use cocoalumberjack 2.0.0-beta4. See https://github.com/seltzered/SVGKit/commit/b7808081b1766fc0a1e8b81e936f072a0d5e69b0 for a detailed note on how I added this via git subtree.

I was a bit torn between whether to do it this way or pullreq the method done via just adding a podfile -- this seemed lower risk for now and for those not using cocoapods. I do have an experiment via the podfile method in https://github.com/seltzered/svgkit/tree/Lumberjack-2.x-svgkit-experimental