Feature release 2.1.0

• Custom callbacks with dnd-callback: The new dnd-callback attribute allows for communication between the source and target scopes. For example, this can be used to access information about the object being dragged during dragover, or to transfer objects without serialization, which allows to use complex objects that contain functions references and prototypes. Demo
• Drop effects fixed and extended: Most of the bugs around drop effect have been fixed. You can now use move, copy and link, or a combination of them. Drop effects can be restricted using dnd-effect-allowed on both the source and target element, and if there are multiple options, the user can choose one using modifier keys (Ctrl or Alt). See the design document for more details. Drop effects don't work on IE9. They do work accross browser tabs if dnd-external-sources is activated, although the source restrictions are lost in Safari and IE.
• New dragleave handler: Previously, the dragleave handler used a timeout to determine whether the placeholder needs to be removed from a dnd-list. The new implementation utilizes document.elementFromPoint to determine whether the mouse cursor is outside the target list.
• Remove dndDraggingSource without timeout: Fixes problems with ngAnimate (#121).