Make --help output go to standard output.

A program's help text, when requested by the user, is not an error
message.  Kind of silly to direct it to the standard error stream.

Adjust the program so that help text goes to standard output, which
is consistent with the GNU coding standards.

For actual errors, print a simplified usage message to standard
error instead of the full help text because otherwise the actual
error message is going to scroll right off the screen.