--------------------
This patch improves our error and warning messages.
- Add a warning for ``st.text("ascii")`` - you probably meant ``st.text(st.characters(codec="ascii"))``. Similarly for ``"utf-8"``.
- Recommend remedies in the error message of ``Unsatisfiable``.
- When ``given`` errors because it was given an extra keyword argument, and the keyword matches a setting name like ``max_examples``, recommend ``settings(max_examples=...)`` instead.