`@flatten` Flattens an array with child arrays.
[1,[2],[3,4],[5,[6,7]]] -> [1,2,3,4,5,[6,7]]
The {"deep":true} arg can be provide for deep flattening.
[1,[2],[3,4],[5,[6,7]]] -> [1,2,3,4,5,6,7]
The original json is returned when the json is not an array.
`@join` Joins multiple objects into a single object.
[{"first":"Tom"},{"last":"Smith"}] -> {"first","Tom","last":"Smith"}
The arg can be "true" to specify that duplicate keys should be preserved.
[{"first":"Tom","age":37},{"age":41}] -> {"first","Tom","age":37,"age":41}
Without preserved keys:
[{"first":"Tom","age":37},{"age":41}] -> {"first","Tom","age":41}
The original json is returned when the json is not an object.
`@valid` Ensures that the json is valid before moving on. An
empty string is returned when the json is not valid, otherwise
it returns the original json.
This modifier returns the current element as-is and can be used
to retrieve the JSON document itself. It is equivalent to the `#/` JSON Pointer.
Closes#149
