parse(FILE*) is a minor overload, but dispatching strerror takes too
much cost. Standard library version is not thread-safe, so some compiler
reports a warning. There are thread-safe versions defined in XSI, GNU,
and Windows. XSI/GNU versions can be detected by macros, but in some
cases, detection-by-macro written in the doc does not work.
Since errno can be obtained from the exception, users can call strerror
that is available in their env if needed. We can just report errno.
The fstream classes are notorious for their non-existent error handling.
This adds a C-style fILE * IO (fopen(), etc.) alternative interface, so
that if a user needs reliable error handling, they can use that, albeit
more inconvenient, but more robust approach.
