Nomenclature for maintainers/collaborators

[twofaktor]

• Concept ACK - Agree with the idea and overall direction, but haven't reviewed the code changes or tested them.
• utACK (untested ACK) - Reviewed and agreed with the code changes but haven't tested them.
• Tested ACK - Reviewed the code changes and verified the functionality or bug fixes.
• ACK - A loose ACK can be confusing. It's best to avoid them unless it's a documentation/comment only change in which case there is nothing to test/verify; therefore the tested/untested distinction is not there.
• NACK - Disagree with the code changes/concept. Should be accompanied by an explanation.