Support RO-Crate 1.3 specification #258

This only has one real change - updating bioschemas term mappings in the context - so hopefully a fairly straightforward upgrade. I'm not sure if those are even directly used in this library.

https://www.researchobject.org/ro-crate/whats-changed-in-1-3

• add 1.3 to version selector
• ensure that features that work for 1.2 also work for 1.3 (e.g. making detached crates)