Grunt

Migrated the build to use Grunt, removed the jar files and ant related stuff and added a build task to automatically copy the dev version of Pixi to the examples and updated the docs to reflect the new build process.

I added a jshint task but this always fails due to the number of complaints it makes. It is disabled for now. It can be run manually with `grunt jshint`. 

A few improvements that could be made would be adding a version number and copyright notice to the bin files it outputs. This version number would come from what's in the package.json. Leave that for Matt to decide :)