Make it easier for implementers to know what's changed

[jpmckinney]

The types of changes to indicate might include: "add", "remove", "deprecate", or otherwise "change". This might involve adding version numbers to +the documentation of+ codes and fields , as new columns or properties. We might, more broadly, consider other improvements to how we communicate changes.

Python's documentation has, for example, "New in version 3.2" and "Changed in version 3.5: …". We can look at how other standards communicate changes in a structured way (e.g. ISO codelists).

This would support implementers to: be aware of changes, adopt new terms, re-code deprecated terms, update data entry forms, etc.

(This issue is based on a conversation about master data management at a February 2018 workshop.)

[jpmckinney]

See IATI's migration documentation: http://reference.iatistandard.org/203/upgrades/integer-upgrade-to-2-01/migrating/

[jpmckinney]

Sphinx has versionadded and versionchanged directives.