Fixes multiple copyright messages in the doxygen docu.

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

Dmitri Naumov authored 5 years ago and Tom Fischer committed 5 years ago

This avoids the mutable member. The data is computed
on every call anyway.

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.