Especially useful when all nonlinear iterations should
be output. See <output_iteration_results> tag.

Fix warning readability-inconsistent-declaration-parameter-name.

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

Include spdlog via BaseLib/Logging.h, which
provides macro replacements for
ERR/DBUG/WARN/INFO...

Most of the current .clang-tidy contained checks:
google-explicit-constructor
google-readability-braces-around-statements
modernize-loop-convert
modernize-use-default-member-init
modernize-use-emplace
modernize-use-using
readability-braces-around-statements
readability-else-after-return
readability-named-parameter
*readability-namespace-comments
*readability-inconsistent-*
readability-redundant-member-init
readability-simplify-boolean-expr
readability-string-compare
*explicit-conversions*

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

The move ctor is not implemented in gcc < 5.

The reinterpret cast seems to more appropriate in context
of writing of binary values to a stream.

Clang format run on near-the-header lines.

Happy New Year

Writes output files to the specified output directory.