Substitute mode for json-iter

[amarao]

Found need for 'substitute' mode - add/replace element of object (inside array) based on output of program with specified args.

Example: [ { "uuid": , "data": }, ... ]

cat example.json|json-iter --substitute --key-name='owner' get-owner {.uuid}

result:

[ { "uuid": , "owner": , "data": }, ... ]