QxExtras : QxOrm library extra-tools (for example : enable std::optional for C++17 compilers, enable boost::optional feature without enabling all boost features)

Files
file	QxStdOptional.h
	Support std::optional<T> class (requires a C++17 compiler) to manage NULL database value, this header should be included just after <QxOrm.h> header file (ideally in a precompiled header)