Add --newer and --different to get command

[gholt]

These are great for put and should be added to get.

[chriswheeler]

Is this project still active, or is there a better alternate? I'd love to have the newer/different options for get. If there are no better alternates I'll have a go at adding them my self and make a PR if I can get them working :)

[gholt]

The project isn't horribly active, but I do try to maintain it as others submit patches. I'm not aware of great alternatives. I thought there was one written in Go, but I can't find it now.