Add remove() and __unset(), update JsonPath

[dafeder]

This adds a remove() method, which is just a wrapper for JsonPath::remove, and also an magic __unset() method that attempts to unset a property using remove(). Both will validate before modifying the object.

So we can do on the following:

{
  "field1": "foo",
  "field2": "bar"
}

1. $rootedDataObject->remove("$", "field2");
2. unset($rootedDataObject->{"$.field2");

Either will result in:

{
  "field1": "foo",
}

Also updates to latest release of JsonPath library.