Allow json{b}_strip_nulls to remove null array elements
 
An additional paramater ("strip_in_arrays") is added to these functions.
It defaults to false. If true, then null array elements are removed as
well as null valued object fields. JSON that just consists of a single
null is not affected.
 
Author: Florents Tselai <florents.tselai@gmail.com>
 
Discussion: https://postgr.es/m/4BCECCD5-4F40-4313-9E98-9E16BEB0B01D@gmail.com