v1.0 - Doc Updates

[DougHamil]

To prepare for the v1.0 release update the documentation:

• [x] ISystem usage
• [x] IEntityType and IUpdateableEntityType usage
• [x] threeagent.core/render usage
• [x] Add doc-strings to all built-in elements
• [x] Context usage
• [x] :ref, :on-added, :on-removed usage
• [x] Migration guide for v1.0