Adds grunt task runner.

Thank you to @SirRawlins for the suggestion in issue #3.

Grunt tasks added;
- Linting the JS.
- Minifying the JS.
- GZipping the JS.
- Bumping the version number. (inc jquery manifest) / Tagging a release. (grunt bumper:<major/minor/patch>)
- Pushing latest example to GHPages. (grunt push-demo)
- Local web server (grunt server)