v0.10.0 - Minor fix to custom elements

Improved implementation for custom elements: there are no more container elements on the DOM for every custom element.

To register a custom element, you must provide a View, not just a DataFlowNode. This is minor breaking change. You need to replace Cycle.registerCustomElement('my-element', SomeDataFlowNode) with Cycle.registerCustomElement('my-element', SomeView).