tagging convention for OpenCL ecosystem repos

This issue is a follow-up from the December 2020 maintenance release: https://github.com/KhronosGroup/OpenCL-Docs/issues/528.

Many of the OpenCL repos use a date-based tagging scheme but the spec and the C++ bindings use a version-based tagging scheme. Should we adopt a consistent tagging scheme for all of the OpenCL repos? If so, which tagging scheme should we adopt?

Start by reviewing the linked follow-up issue, OpenCL-Docs#528, and comparing the date-based and version-based tags used across the OpenCL repositories. Done means the ecosystem has an agreed tagging scheme and a documented decision about which convention to adopt.

Written by the indexing model from the issue text.