Rules-based mulliganning

[hitz]

There should be support for supplying rules for mulliganngin. This would have to be for a specific deck (constructed) but could also be general (N castable spells).

Using some off the shelf rules logic system might make sense here. The "rules" hook is currently in players.py but perhaps should be in decks.py or some deck specific config.

Some starting points:

• https://github.com/venmo/business-rules
• https://github.com/jruizgit/rules
• http://pyke.sourceforge.net/