Exit status

[tansy]

There should be exit status returned on success and on error. I tried to test it but there is no way to do it as it always returns 0, which in this context doesn't mean anything.
I think lzip does it right, returning 0 on success, as other programs and non zero on failure.

Exit status: 0 for a normal exit, 1 for environmental problems (file not found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or invalid input file, 3 for an internal consistency error (eg, bug) which caused lzip to panic.

This could not only give indicator of error but let to test it in automatic way.