Add grunt + a "release" task to automate version releases

Usage (after npm install -g grunt-cli):
* grunt release (defaults to patch release, 0.0.1)
* grunt release:minor (0.1.0)
* grunt release:major (1.0.0)

Steps:
* Updates version in package.json
* Adds/commits/tags in repo
* Pushes to GitHub (including tags)
* Publishes to NPM
Merge pull request #10 from tinyspeck/grunt-release

Add grunt + a "release" task to automate version releases