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