Fix type in init of OMS families
Fix name of __call__ in category framework. Implement call for modular symbols.
Fix instantiation of factories.
And so pickling the spaces should now work. Add doctests to show so. (There is a bunch of commented out stuff; a relic of the painful process of making pickling work).
Make pickling of elements work and test it. (Again, some in the end unnecessary code has been commented out).
Update some families of distributions elements doctests after having made that minor change to the filtration.