boost::none -> std::nullopt
boost::make_optional -> std::make_optional
boost::optional<T>::get() -> std::optional<T>::value()

Fixes multiple copyright messages in the doxygen docu.

ag '\\file' -L --ignore=ThirdParty *Lib |xargs  sed -i 's/\(.*\)\\copyright/\1\\file\n\1\\copyright/'

Only in ERR/WARN/INFO/DBUG/OGS_FATAL and similar, not in
formatted output like xml files.

Update documentation mismatches in other getConfigAttribute*().

Clang format run on near-the-header lines.

Happy New Year

This potentially saves a second copy compared to using const
reference. See Effective Modern C++, Item 41.

Christoph Lehmann authored 8 years ago and Dmitri Naumov committed 8 years ago

Returns boost::none in the case of error.

const + mutable enable use as temporary variables
move assignment complements move construction