This introduces two new JSON utility functions, json_get_pointer_info

and json_resolve_pointer, which are used to return information from a

JSON-compatible object based on a JSON Pointer path. These paths are a

standard way of specifying a location within an object, supporting

dictionary keys, array indices, and even an "end of array" marker (for

insertion purposes in other functions).
json_get_pointer_info attempts to resolve as much of the specified

path as possible, returning information on what was able to be resolved,

what remains, and what error should be shown if expecting a

fully-resolvable path. It's useful for cases where the path being used

may not necessarily have to represent an existing location in an object.
json_resolve_pointer takes a fully-resolvable Pointer path and returns

the value from the object that it matches. If the path cannot be

resolved, an exception is thrown. This is intended for use in the more

common cases of simply needing to access data from an object.

Unit tests passed.