remove `extend` from the global object

[bloodyowl]

if you want to use modular JavaScript, use browserify and compile with grunt, but don't expose this method. https://github.com/HugoGiraudel/CRUD.js/blob/master/src/helper.js#L4

[KittyGiraudel]

Good point, I'll see what I can do.

[MoOx]