This is a new error which implements the restic.Fataler interface.
Errors of this type are written to stderr, the restic exits. For all
other errors, restic prints the stack trace (if available).
The windows cmd shell is not aware of ANSI escape sequences and
does print them uninterpreted to the console. This is ugly.
Added a function to generate platform specific string for the escape sequence. On Windows this will be 79 white spaces with
a trailing \r.
