v0.6.1

This release updates the grammar to match rzk v0.11.1, which adds higher inductive types.

• Highlight the re-ascription clauses eliminate with and compute with, which replace the eliminator clause of rzk v0.11.0.
• The into motive of a modal let mod needs no grammar change: into was already a keyword for match.
• Cover the new syntax in the tests: the circle with a path constructor and both re-ascription clauses.