Implement failing test for group.position after content changed.
Fix issue with group.position not updating when content changes.
Clean up strange constructor notation that causes linting issue.
Implement registration point for all items.

Allowing any item to use another point than the center as its anchor point for item.position.
Put constructors into separate ctor variables when handling dontLink parameters before creating objects.

This hopefully solves the mysterious issue #360 on Chrome.
Merge git://github.com/paperjs/paper.js