------
- First appearance of Parameter.set_constraint().
- Previously Parameter constraints were limited to algebraic Python
expressions. Now Parameter.set_constraint can be given a callable which
is evaluated at runtime, allowing more sophisticated constraints to be
developed. (N.B this is separate to the inequality constraints that can
be made during curvefitting using the NonLinearConstraint machinery).
- Add a Parratt recursion for calculating reflectivity, it seems to be a
little faster.
- Ported the pymc wrapper from pymc3 --> pymc (v4), which was released in
Jun2022.
- added sequence_to_parameters function.
- added LipidLeaflet.make_constraint.