v0.17.0

This release implements STAM v1.2.

New

• core: Added a `DataValue::Map`` type, supporting arbitrary nested maps
• core: Added `DataOperator::GetKey`` to access keys in maps
• query: Added . operator in to access keys in maps
• web annotations: implemented conversion of maps
• web annotations: allow specifying JSON-LD contexts and using STAM keys as aliases.
• web annotations: added skip_context parameter to skip serialisation of JSON-LD contexts, useful in situations where it is already done in a prior stage.

Bugfixes

• web annotations: prevent duplicate anno.jsonld in context and map rdfs:type properly without full IRI

Other

• extra tests
• dependency updates