Stam

* Stricter definition of relative paths in `include` mechanism, don't leave it to the implementation.

* STAM Core:
* Allow adding other annotations stores as dependencies (aka substores) 29
* Removed DataValue::Id (was never used)
* Better documentation for public identifiers
* STAM Query Language:
* Allow multiple subqueries 28
* Added LIMIT keyword 25
* documented ADD and DELETE statements 23
* documentation improvements 23
* STAM Validation:
* recommend either checksum or text based on text length
* STAM Transpose: Added "regsegmentation"
* STAM Web Annotations: updated and rephrased

Formal first release of the STAM specification.

Implemented in stam-rust 0.9.0, stam-python 0.4.0, stam-tools 0.4.0.

Bugfix release and minor API change:

* implemented STAMQL serialisation of collection constraints that were not serialisable before
* DataOperator::Equals now takes Cow<'a, str> instead of &'a str, so it can be owned or borrowed: If in your code you use `DataOperator::Equals("blah")` you will now have to change it to `DataOperator::Equals("blah".into())`

Bugfix release:

* query: added a missing constraint
* query: do not propagate NotFoundError and (new) VariableNotFoundError in UNION

Dependency downgrade of minicbor so things keep running on slightly older rust versions