stopped grunt from executing during install

Instead of generating the `lib/*.js` javascript from the `src/*.coffee` files during install, they are generated before this package is published. This means that installation is a little quicker and simpler for all users and is [recommended by npm](https://www.npmjs.org/doc/misc/npm-scripts.html#NOTE-INSTALL-SCRIPTS-ARE-AN-ANTIPATTERN).

As a bonus, grunt and its plugins are just dev dependencies. Also, unlike #40, the generated `lib/*.js` files do not need to be checked in.