adds helper to hold intermittent results of deref
adds helper to hold intermittent results of deref

For things like filter that may need to dereference multiple times.
Doing so violates the input_iterator guarantees.

tempbottle/cppitertools,ryanhaining/cppitertools,tempbottle/cppitertools,ryanhaining/cppitertools,jkhoogland/cppitertools,ryanhaining/cppitertools,jkhoogland/cppitertools,jkhoogland/cppitertools,tempbottle/cppitertools