0.4.0 Backward incompatible changes: * The _format_json function now requires nested calls to live inside quotes. See `ok.sh help _format_json` for a usage example. Misc additions and fixes: * Fix a regex bug with mawk (thanks, dubiouscript!). * Fix several script breakages in a Busybox environment. * Add a Docker file for quick local development and testing. * Add several commands to the Makefile to streamline development. * Update hardcoded VERSION value in the script. * Add more information to CONTRIBUTORS doc.