google cloud support

[theromis]

Cherry pickled just GCS commit, but I need instructions about adding/updating dependencies in the vendor folder

example conf

{
  "port": 3001,
  "storage": {
    "dst": {
      "type": "gcs",
      "location": "gocache",
      "cache_control": "max-age=86400",
      "bucket_name": "bucketName",
      "base_url": "https://example.com",
      "secret_access_key": "/path/to/google_creds.json"
    },
    "src": {
      "type": "gcs",
      "location": "",
      "cache_control": "max-age=86400",
      "bucket_name": "bucketName",
      "base_url": "https://example.com",
      "secret_access_key": "/path/to/google_creds.json"
    }
  },
  "kvstore": {
    "type": "cache"
  },
  "shard": {
    "width": 2,
    "depth": 2,
    "restonly": true
  }
}

PS: go build perfectly compiles for me

[thoas]

This PR will be merge after #114, gostorages will be updated then.