Add a verbose flag to 'save' operation

I've developed that to have an overview of what was happening
when running godep, it's still a bit drafty.

Sample output:

```
$ godep save -r -v
import-path:	 github.com/Soulou/sample-project
go-version:	 go1.3.3
dependency:	 bitbucket.org/tebeka/strftime 2194253a23c090a4d5953b152a3c63fb5da4f5a4 0.1.2-4
dependency:	 github.com/AlekSi/airbrake-go 93a91a338f77e7bcf1447c4ae3afe848d62a45cd
dependency:	 github.com/Scalingo/go-etcd-lock/lock a39e1fe285d1134060650a3dc4284203614ecdf3 v0.2-2-ga39e1fe
new dependency:	 github.com/Scalingo/gopassword 5e9b4ab86ad3f192d3b75b36f4e6efef4eadcccf
new dependency:	 github.com/Scalingo/logrus-airbrake 240f37235524a9567ec922948c458a87fda2f9e0
dependency:	 github.com/Sirupsen/logrus c13432b0a52fa22ed08301e522a0bdb2ce0e2d40 v0.5.1-2-gc13432b
dependency:	 github.com/Soulou/acadock-monitoring/client f51550868981f956fba95beaac4f425261c29bda v0.1.1
dependency:	 github.com/codegangsta/inject 4b8172520a03fa190f427bbd284db01b459bfce7 v1.0-rc1-4-g4b81725
dependency:	 github.com/coreos/go-etcd/etcd 23142f6773a676cc2cae8dd0cb90b2ea761c853f v0.2.0-rc1-120-g23142f6
dependency:	 github.com/go-martini/martini 7d32ea3fa6590565c928b90a48178b60b96df98f v1.0-50-g7d32ea3
dependency:	 github.com/gorilla/handlers 0e84b7d810c16aed432217e330206be156bafae0
dependency:	 github.com/lib/pq c6325123e6d45115749734a8bc35060ebac74d0e
dependency:	 github.com/martini-contrib/auth 7925ee933d02cb66101819126f8b39367994c2b2
dependency:	 github.com/robfig/cron b024fc5ea0e34bc3f83d9941c8d60b0622bfaca4 v1-3-gb024fc5
dependency:	 gopkg.in/Scalingo/etcd-discovery.v2/service 191c3af21099f20b41d8486b9310ceeff78fd168 v2.0
dependency:	 gopkg.in/errgo.v1 1a3d4d77253d47458a42542b4c0bf709fcd5d715
dependency:	 gopkg.in/mgo.v2 c9fd3712fbf3e92924c974dce16da2d322508fe2
copy:	 /home/leo/Projects/Go/src/github.com/Scalingo/gopassword → Godeps/_workspace/src/github.com/Scalingo/gopassword
copy:	 /home/leo/Projects/Go/src/github.com/Scalingo/logrus-airbrake → Godeps/_workspace/src/github.com/Scalingo/logrus-airbrake
rewrite Godeps/_workspace/src/github.com/Scalingo/logrus-airbrake/examples/test.go:
  "github.com/AlekSi/airbrake-go" → /home/soulou/go/src/github.com/Scalingo/appsdeck-database/Godeps/_workspace/src/github.com/AlekSi/airbrake-go
rewrite Godeps/_workspace/src/github.com/Scalingo/logrus-airbrake/examples/test.go:
  "github.com/Sirupsen/logrus" → /home/soulou/go/src/github.com/Scalingo/appsdeck-database/Godeps/_workspace/src/github.com/Sirupsen/logrus
rewrite Godeps/_workspace/src/github.com/Scalingo/logrus-airbrake/hook.go:
  "github.com/AlekSi/airbrake-go" → /home/soulou/go/src/github.com/Scalingo/appsdeck-database/Godeps/_workspace/src/github.com/AlekSi/airbrake-go
rewrite Godeps/_workspace/src/github.com/Scalingo/logrus-airbrake/hook.go:
  "github.com/Sirupsen/logrus" → /home/soulou/go/src/github.com/Scalingo/appsdeck-database/Godeps/_workspace/src/github.com/Sirupsen/logrus
```

What do you think about that? What would you display?