GuessPluginTypeFromLibPath() was previously testing the type, but also the
existence of the lib file of *.kicad_sym filename, but when creating a new lib,
its existence obviously must not be tested
GuessPluginTypeFromLibPath() was previously testing the tye, but also the
existence of the lib file, but we only need to know the plugin type of
the given file, regardless it exists or not.
Recommendation is to avoid using the year nomenclature as this
information is already encoded in the git repo. Avoids needing to
repeatly update.
Also updates AUTHORS.txt from current repo with contributor names
The IO_RELEASER is a thin-wrapper around a std::unique_ptr, but done
this way to allow easier addition of a custom deleter in the future if
something needs to call back into the IO_MGR.
