Add a more ergonomic structure to represent the changes structure

[NullVoxPopuli]

Reference: https://runkit.com/nullvoxpopuli/how-to-use-changeset-data-and-changes

instead of .changes being:

[ {key: "foo", value: 1}, Object {key: "bar", value: "there"}, …]

it should be something easier to understand in isolation, like:

{
  "foo": {
    original: 0,
    current: 1,
  },
  "property.path.0.deep": {
    original: 'hello',
    current: 'there'
 }
}

now, this can easily be computed from the existing .changes, but I think because it is a common desire to build this structure, it should be provided out of the box. maybe via:

changeset.changedValues;

[snewcomer]

This seems like a good suggestion. We could start with changedValues and do a switcharoo with changes in a major. I'm in favor