Advanced path string syntax for slicing

[bauerca]

Currently, only one value can be extracted from a JSON stream; for example, fetching 2 values from a large array requires two stream passes. A JSON path string syntax for complex slicing would allow extracting multiple values from a single stream.

Some things to consider:

• Output order must match order in stream. (requesting, for example, [arr[1], arr[0]] is impossible)
• Other things. :)

An enhanced path string could basically be JSON where values are path strings. For example:

{"dogs": dogs[0:3], "cat_breeds": cats[:].breed}

where the example also introduces an array slicing syntax similar to python and a map function that allows picking attributes over an array of objects.