Prepare for publishing to NPM

* Update `package.json`:
  * Add `main` field, pointing to CommonJS build at `dist/route-recognizer.cjs.js`.
  * Update description.
  * Add version -- I chose `0.1.0` but perhaps it should be different.
* Add `.npmignore`, ignoring Ruby build files.
Merge pull request #16 from spikebrehm/prepare-for-npm

Prepare for publishing to NPM