Allow combinations of blendMode and opacity.

Closes #259.
Add support for canvas compositing modes to Item#blendMode.

Closes #159.
Avoid use of 'window' for Node, and pass on reference to root scope instead.
Use fire('frame') instead of onFrame(), to correctly handle frame events on Node.
Fix faulty comment about _handleFrameItems.
Separate requesting and handling of animation frames.

Closes #176.
Add support for shadows.

Closes #36.
Only test for fill in Item#_hitTest() if options.fill is set.
Define failing test about Item cloning hierarchy.

Cloned items should be inserted right above their originals.
Implement insert parameter in Item#clone() to control DOM insertion.

Defaults to true. Also insert in the right place now, above the original.
Fix active layer test when calling Layer#clone().
Use insert: false option in creation of all clones.

Still needs implementing in Item constructor.
Filter out the insert parameter in _set for now, to prevent issues with cloning().

Work in progress.
Do not insert boolean operation clones into DOM.
Allow Base#_set() to exclude properties.
Allow Item#_changed() to function before #_project is set.
Move and unify handling of Item#_set(props) to new Item#_initialize(), and add support for props.insert = false.
Fix avoiding of name clashes in cloning.
Improve tests for moveAbove() / moveBelow().
Use non-deprecated versions.