Add an error handling feature to every input and output functions;

Fix a part of identifiers not to violate the C++ standard

In addition to fopen(), malloc(), etc., the functions fclose(),
fgetc(), fputc(), fputs(), and fprintf() are also replaced with their
respective wrapper functions that handle errors.
This replacement is done only where they are used for parsing or code
generation, and is not done for message printing and debug dumping.

Every double underscore __ contained in an identifier that consists of
uppercase letters and underscores (e.g. STRING_FLAG__IDENTIFIER) is
replaced with a single underscore (e.g. STRING_FLAG_IDENTIFIER),
not to violate the C++ standard ISO/IEC 14882-2014.
It states "Each name that contains a double underscore __ or begins
with an underscore followed by an uppercase letter is reserved to
the implementation for any use."