Release 0.12.0

• Provide a way for elements to mark attributes as unrefracted arrays of
  refracted elements. Subclassed elements can push onto the
  _attributeElementArrayKeys property to use this feature. Note: in the
  future this feature may go away.

• Allow load to be used for plugins where a namespace is not being used

• Add an elements property to the Namespace class which returns an object of PascalCased element name keys to registered element class values. This allows for ES6 use cases like:

  const {StringElement, ArrayElement, ObjectElement} = namespace.elements;

• Add functionality for Embedded Refract