Add 'vdi-similar-content'

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Add vdi-compose

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Update ChangeLog

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #2 from djs55/similar-content

Add vdi-similar-content and vdi-compose