Add ability to have coded game families and filter by Game metadata

[edwardchalstrey1]

Issues closed by this PR

Closes #758
Closes #759

Description of the changes in this PR

This PR adds

• The option to generate games for the catalog from code via game family functions (and add as many variants as you want)
• The ability to filter the catalog search on attributes of Game objects
• Adds to the documentation: pygambit API reference for catalog functions

How to review this PR

• Check whether adding to families.py works as a way for adding games to the catalog. Review the change to the contributor doc which explains how to do this.
• Review the updates to the games() function which allow filtering on attributes of Game objects

Help me answer these questions:

1. I have added one_shot_trust as an example game family in this PR, simply to demonstrate the functionality. Is there a better example we definitely want included in the catalog?
2. I think I will open a new issue after closing [Catalog] Search feature #759 to add the ability to filter based on metadata not associated with a Game object, to be looked at once the catalog is larger, if at all. Do you agree with this/ do we need it at all? If so, what is an example of a filter that would be useful when searching the catalog?

[tturocy]

@rahulsavani @edwardchalstrey1 are we thinking of this as something for 16.6 or more for 16.7 once we let the catalog settle a bit and get it populated more? (And also because we've got a backlog on 16.6 to deal with so at least for my part I'm a bit limited in mindspace as to how we might want to commit to some of these design decisions.)

[edwardchalstrey1]

@rahulsavani @edwardchalstrey1 are we thinking of this as something for 16.6 or more for 16.7 once we let the catalog settle a bit and get it populated more? (And also because we've got a backlog on 16.6 to deal with so at least for my part I'm a bit limited in mindspace as to how we might want to commit to some of these design decisions.)

@tturocy Fine with me, I'll move this back to draft for now