#558 tagUsage/@render should be deprecated

[Martin Holmes]

Per FR 520:

https://sourceforge.net/p/tei/feature-requests/520/

we [will] now have a better way of providing default rendition declarations for elements. Syd suggests that we deprecate the existing tagUsage/@render, and provide a stylesheet for converting it to the equivalent rendition+@selector representation.

[Hugh A. Cayless]

This seems uncontroversial to me. Any objections? Assigning to Syd.