* feat: --skip-hardlinks flag
Adds a --skip-hardlinks flag that will not process any files that have an active hardlink.
Without a pre-scan to identify hardlink targets and relink them after copies, all this would result in is duplication.
You'd then have to run another de-duplicator, which doesn't have knowledge of the balancing, and could arbitrarily undo
the balancing work.
* doc: .rebalance suffix -> .balance suffix
* doc: add --skip-hardlinks parameter to README
* test: add unit tests for --skip-hardlink
