use different ImageMagick library?

Met @maxim the other day after giving a talk about magickly, and he suggested using Skeptic as the ImageMagick (which I'll call "IM") wrapper.

I haven't been actively working on magickly in a while, and haven't been following progress on IM Ruby libraries. The issue with Dragonfly 0.x (not sure about 1.x) is that each transformation is applied in a separate convert command

• Use the single-convert changes done by @tolsen forever ago
  • Would want to do some cleanup/documentation before merging in – see https://github.com/afeld/magickly/issues/16
  • Ideally this logic would be at the IM wrapper level, keeping magickly simple
• Use RMagick
  • All in memory (not sure if this is a good or bad thing)
  • Read veeery mixed reviews about it when first building magickly and deciding what to use (e.g. memory leaks), though this may have improved since
• Use Skeptic
  • From a quick glance, seems well-thought-out, and well-suited to keeping magickly easily extensible.
  • The DSL could make the existing shortcuts a lot more readable.
  • Doesn't do argument format enforcement – ideally this would be outside magickly as well
  • Only runs a single convert command (correct @maxim?), so theoretically should have the same performance characteristics as single-convert

Feedback/ideas welcome!

P.S. This change would obviate https://github.com/afeld/magickly/issues/48.