Remove unused version of findElementOrError with iterators
and error string.

Using in MPL shows no difference in runtime, one assembly
instruction is different.

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

The fmt library happily accepts std::string without
any conversions.

StringTools.h and FileTools.h mostly. fstream in few places.

Mostly in the file headers.

find *Lib -type f | xargs sed -i 'N;s%^\s\+\*\n\(\s\+\*/\)%\1%'

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

This is a variation of getOrError() for containers using a predicate.

Also drop the unnecessary 'inline', because of a template function.