Merge pull request #22 from mistifyio/cleanup

golint cleanup
Merge pull request #24 from Mic92/master

 Additions from docker/zfs (take 2)
Just test if logical used is greater than 0, as this appears to be implementation specific
add docs to satisfy golint
Merge pull request #21 from mistifyio/devel

Place holder PR for merging devel
need to return the error here
Merge pull request #25 from mistifyio/return-error

need to return the error
zfs diff handle hardlinks modification now