This function opens a file,
in the mode specified in the string
It returns a new file handle,
or, in case of errors, nil plus an error message.
mode string can be any of the following:
- "r": read mode (the default);
- "w": write mode;
- "a": append mode;
- "r+": update mode, all previous data is preserved;
- "w+": update mode, all previous data is erased;
- "a+": append update mode, previous data is preserved,
writing is only allowed at the end of file.
mode string can also have a '
b' at the end,
which is needed in some systems to open the file in binary mode.
This string is exactly what is used in the
standard C function