Support jsonpath functions

[lu-zero]

Problem to solve

Sometimes would be useful to select the max(),min() or even produce a sum() over a returned array and potentially also capture it.

Proposal

Implement the jsonpath functions min(), max() and potentially also the ones described in the rfc.

Additional context and resources

The jsonpath rfc lists the following functions:

• length()
• count()
• match()
• search()
• value()

Tasks to complete

• Add the machinery to support functions
• Implement a fixed set of functions
• Allow defining additional functions in Options

[fabricereix]

Thanks @lu-zero for your issue.
We should indeed implement the full RFC.