Add deferred flag to zfs.Destroy()

Signed-off-by: Jörg Thalheim <joerg@higgsboson.tk>
add Logicalused property
Add Origin property

Signed-off-by: Jörg Thalheim <joerg@higgsboson.tk>
gofmt

Signed-off-by: Jörg Thalheim <joerg@higgsboson.tk>
Add zfs.Diff

Signed-off-by: Jörg Thalheim <joerg@higgsboson.tk>
Add Logger
add recursive destroy with clones

Signed-off-by: Jörg Thalheim <joerg@higgsboson.tk>
use CamelCase-style constants
Merge pull request #24 from Mic92/master

 Additions from docker/zfs (take 2)