Standardize `summary()` invisible returns

[christopherkenny]

summary() has different things returned (invisibly) after printing. It seems like it would be good to standardize what gets returned a bit. For example, for flip or mergesplit, if rhats are computed, they get returned. For SMC, even when they are computed, only efficiency stats are returned. We could improve this by adding more info in the return, possibly:

• return a list of stats by type
• make a tibble with list columns for the types of stats
• add columns for rhats (repeated each time, e.g. rhat_column_name?)

This helps us standardize some diagnostic tables downstream to try to make sure people are running summary() whenever they use multiple chains (which they should do for most purposes).

[christopherkenny]

@CoryMcCartan, do you have any thoughts on this?

[CoryMcCartan]

Yeah, should be a list rather than a data frame probably

One entry of the list would be e.g. rhats

Others would be acceptance rate, various efficiency stats, etc.