Add support for an object-based JSON format for entities

[bruth]

The motivation for this is to support slightly more familiar format that is less verbose to produce than raw facts. In addition, there are many workflows where facts are being generated from existing objects so this is convenient format to map to.

The proposed format is below:

{
    // Optional valid time of the facts.
    "time": null,

    // Optional embedded domain of the facts.
    "domain": "users",

    // Optional operation which defaults to "assert". If "retract" is used all
    // of the derived facts will be retracted.
    "operation": "assert",

    // The identity of the entity the attributes are associated with. If
    // no domain is encoded in the identity, it will use the embedded
    // domain if one is supplied.
    "entity": "bob",

    // Attribute-value pairs of the entity. All will be parsed therefore
    // references (such as `users/sue`) must have an explicit domain.
    "attributes": {
        "origins.attrs/label": "Bob",
        "name": "Bob",
        "mobile": "555-1234",
        "spouse": "users/sue"
    }
}

This would be expanded into the following set of facts:

domain	operation	valid_time	entity_domain	entity	attribute_domain	attribute	value_domain	value
users	assert		users	bob	origins.attrs	label		Bob
users	assert		users	bob	users	name		Bob
users	assert		users	bob	users	mobile		555-1234
users	assert		users	bob	users	spouse	users	sue