Nested digests are now possible. See #18

• unidirectional data binding via "link()" #15

• Use strings as ids #13
• Separate id from name in serialization #14

Serialized graphs now look like this:

{
  "nodes": [
    { "id": "95", "propertyName": "fullName" },
    { "id": "96", "propertyName": "firstName" },
    { "id": "97", "propertyName": "lastName" }
  ],
  "links": [
    { "source": "96", "target": "95" },
    { "source": "97", "target": "95" }
  ]
}

• Clean up nodes on destroy() #12
• Add ability to serialize data flow graph #11
• Ownership transferred to datavis-tech #4
• Add diagrams #5
• Overhaul documentation #3

This release changes the auto-digest feature to digest on the next animation frame (using requestAnimationFrame) rather than the next tick (using setTimeout). The purpose of this change is to make it so reactive functions that do DOM manipulation only execute as frequently as necessary to update the display. Doing DOM updates more frequently than every animation does not make sense. For a more detailed discussions about this see datavis-tech/reactive-model#9 (comment)

The value null is now considered as defined, and will be passed into reactive functions. See #1