Optimize the bundled/gzipped size of ylem

Currently ylem is 109K minified / 27.4K gzipped. This was determined by running a build using [this test repository](https://github.com/DesignByOnyx/ylem-build-test), and then running the built code through Google closure compiler.

Here's how that stacks up against others:

| Library | Size (minified / gzipped) | URL |
|---|---|---|
| MobX | 49.1 KB / 14.9 KB | [mobx](https://cdnjs.cloudflare.com/ajax/libs/mobx/4.2.1/mobx.min.js) |
| MobX React | 16.4 KB / 6.2 KB | [mobx-react](https://cdnjs.cloudflare.com/ajax/libs/mobx-react/5.1.2/index.min.js) |
| Redux | 6.2KB / 2.5KB | [redux](https://cdnjs.cloudflare.com/ajax/libs/redux/4.0.0/redux.min.js) |
| Redux React | 12.5 KB / 4.5 KB | [redux-react](https://cdnjs.cloudflare.com/ajax/libs/react-redux/5.0.7/react-redux.min.js) |

MobX total: 21.1KB
Redux total: 7KB

Start by reproducing the build with the linked ylem-build-test repository, then run the generated code through Google Closure Compiler as described. Compare the minified and gzipped output with the reported 109K/27.4K baseline; done means reducing the bundle size, though this issue does not identify implementation files or a target size.

Written by the indexing model from the issue text.