* Add support for json output in subkey

* Updates as per code review

* Apply suggestions from code review

Co-Authored-By: Nikolay Volf <nikvolf@gmail.com>

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Clean up error handler as per code review

* Apply suggestions from code review

Co-Authored-By: Marcio Diaz <marcio@parity.io>

* Fix compilation error

* Remove accidental file commit

Co-authored-by: Nikolay Volf <nikvolf@gmail.com>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: Marcio Diaz <marcio@parity.io>