Made sure .find() always returns an instance of List, even when empty
Moved utils.extend to List.extend and fixed a bug, which revealed a whole lot of other bugs in cloning. Fixed by storing all options in this.options
Implemented .remove()
Also added options.source property to support bubbling remove. Closes #9
Added tests for .remove()
Implemented .pop, .shift and .splice
Implemented tests for .pop, .shift and .splice
Merge branch 'remove' into develop