Flag summing

[henryiii]

This is just a note to myself to verify that the generalized flag types from #235 are the best they can be before 1.8.

[phlptp]

One thing I have been wondering is if the default behavior of summing the flags with an integer output should be turned off in favor of take last if flags have a defined default through {xxx} or !. It probably makes sense to keep the summing behavior if all the flags just default to to true for backwards compatibility, but if there are others not sure it makes sense as the default. The callback would still be summing, but it would default to only summing a single element.

[henryiii]

Does anything need to be checked here (such as for summing) or can it be closed?

[phlptp]

I think it might make sense to change the default behavior slightly for the summing flags in 2.0 but otherwise I think it is ok for the time being. I haven't found any oddities in the last couple months.