New options for droplet creations
New options for droplet creations

--ipv6-enabled to to enable ipv6 on droplet creation
--backups-eanbled to enable backups on droplet creation

Special thanks to [@salemine](https://github.com/salemine) [PR #45]
for the backup option.

higanworks/knife-digital_ocean,rmoriz/knife-digital_ocean