Bundle router into a single file

[realityking]

Note that this PR contains 3 parts:

• Update jest to 23.5. This is necessary for my changes to babel to work. (Update jest to 23.5 #143)
• The actual change to the build process
• Adding match and pick to the public API as they otherwise become inaccessible

The primary benefit is that the ESM and CommonJS will be a little smaller because Babel helpers get deduplicated and, when bundling the CommonJS version with webpack, less functions will be created. It also gives Uglify a few more options as less functions are exposed (e.g. startsWith)

It also cleans the project itself a bit up, .babelrc is now a simple JSON file and everything interesting can be found in rollup.config.js.

Downside: The public API is more rigid as only exports from index.js can be consumed

Caution This change is semver major

[ryanflorence]

I appreciate this work, and sorry it took so long to see this, going to close though since we're going to button up the API here soon and messing with the build artifacts is always risky.

For more context: https://reacttraining.com/blog/reach-react-router-future/

Maybe we'll come back to this though, thank you again for your time on this!