Problems with the binomial_primary_decomposition docstring resp. with QQAb printing

[fingolfin]

Two problems with the docstring for binomial_primary_decomposition:

1. It references ζ (zeta), but the code example was changed to use z
2. In the example z actually turns up with two different meanings: once it is a variable in a polynomial ring; and once for a root of unity z(3). I believe that z comes from the QQAb code.

Since z is used a lot in polynomial rings, it seems best if in the printing of roots of unity it is changed to something else, e.g. zeta (spelled out) -- in unicode printing mode it can of course stay as ζ

Secondly, the binomial_primary_decomposition docstring should be adjusted to use that new symbol used for QQAb printing (it could also point to Oscar.with_unicode I guess)

[fingolfin]

This seems to affect more docstrings, in the same file in which binomial_primary_decomposition is defined, e.g.

• cellular_associated_primes
• cellular_minimal_associated_primes
• cellular_primary_decomposition

[fingolfin]

See PR #2491 which just needs to be merged...