Support JSONPath for `_DataLink_` URL format, already supported in JSONLab

[JSONPath](https://github.com/json-path/JsonPath) is a simple format to reference the inner elements of the JSON encoded data, and has been supported in JSONLab (https://github.com/fangq/jsonlab/commit/05edb7adac4c057d7e644ecafe677e3a7959b204).

The `_DataLink_` definition should be updated to support JSONPath flavored data anchor definitions.