Set the default to None - if the ratio does not produce nans then it is
by default used.

and time marg before moving onto dist and tiem nad phase marg

- Add doc file on CBC PE
- Add introduction text

allow aligned spin with a<0

See merge request Monash/tupak!48

Moritz Huebner: Introduced a __repr__format_helper method to help automating __repr__ formatting for all subclasses.

ratio looks a bit off: need to figuring out what's going on with the
normalization