Improved code quality

Hi Ben,

I propose this merge to you : 

- added jshint grunt task
- .jshintrc
- fixed lint error
- build/default d3pie

I use WebStorm as IDE and i can link .jshintrc file to my JSHINT setting. The IDE code editor is then synchronized with the project code quality params.
Now, each grunt alias will run JSHINT first.


thx