cxx14

First of all, great library!

I am having some confusion in understanding the role of values_first2 in set_difference_by_key as mentioned here.

In general terms, the result of set difference D = A - B will not contain values from B therefore values_first2 can never be part of D. So `val

I would like to be able to determine my device-wide primitive's temp_storage_bytes before I have all of the primitive's arguments ready. The interface for obtaining it ostensibly requires everything to be ready for the actual run - and the documentation does not make it clear what arguments it actually needs and what it's going to do with them (e.g. will it look at the input at all, in any way? Pr