lose obsolete MemoryMappedFileReader::GetFileStart/GetFileEnd/GetFileSize (just use begin/end/size())
added new regression test for copy of Optional<Mapping<>> I encountered
minor tweak to Memory::Optional(fix names of operator= members); and fixed very minor bug with types/overloads which caused Optional<Mapping<a,b>>::CTOR (Optional<Mapping<a,b>> () to fail to compile
test for Test_4_Optional_Of_Mapping_Copy_Problem_() was in wrong file - moved - and fixed one bug in test