The tt(std::(experimental::)filesystem) namespace offers its own exception
type ti(filesystem_error). Its constructors have the following signatures (the
bracketed parameters are optional):
        verb(
    filesystem_error(string const &what, 
                    [path const &path1, [path const &path2,]] 
                    error_code ec);
        )
    As tt(filesystem) facilities are closely related to standard system
functions, tt(errc) error code enumeration values can be used to obtain
tt(error_codes) to pass to tt(filesystem_error), as illustrated by the
following little demo-program:
    verbinsert(-s4 //fse examples/filesystemerror.cc)


