JSON Parsing - Counting inside an array, not the array itself

[stevehero]

@Florian, you've implemented this. I forgot I asked for this.

Json_foreach and json_foreach_reverse access counter

This is now available as json_foreach_counter with Mp3tag v3.21b with an option parameter for the number of digits padded with leading zeros if necessary. json_foreach_counter 1 Returns: 1,2,3,4 json_foreach_counter 2 Returns: 01,02,03,04