gklyne/annalist: Annalist release 0.5.8: Subproperty URIs, field description caching, update messages.

This release mainly adds support for sub/superproperty URI relations declared in view field definitions. This is intended to make it easier to work with structured vocabularies like CIDOC CRM, and to facilitate some aspects of data evolution. More details can be found in the "History" section of the latest release notes, previous release notes and via the GitHub issues list