Use browserify to build from CommonJS.

- q.js in the root is now in CommonJS format.
- Running `npm run prepublish` will generate a release folder containing q.umd.js and q.min.js.
- q.umd.js is a "Universal Module Definition" version generate by browserify's "standalone" option, with support for the many module systems and loaders.
- q.min.js is the minified version of q.umd.js.
- Also cleaned up grunt syntax to be less verbose.

Closes #313. The first step toward #280.