Restored (and modified) StoreBoolMap (it was removed in 7ff1c348ae0c)

- also restored _maps_bits::IteratorTraits
- removes the Functor template parameter from StoreBoolMap
- doc changed a bit

EXTRA_DIST += \

        benchmark/Makefile

if WANT_BENCHMARK

noinst_HEADERS +=

noinst_PROGRAMS +=

endif WANT_BENCHMARK