Golang runtime (#125)

Minimal golang runtime.  

Functions are built as Go plugins, and the plugin is uploaded to fission.

See `environments/go/README.md` for instructions and `examples/go` for a usage example.

For now, we're re-using the 'code' field of the function to store the binary plugin. With v2 environments, this will be stored separately as a binary package.

.travis.yml

@@ -16,5 +16,5 @@ script:
    - ./fission-bundle/build.sh
    - hack/verify-gofmt.sh
    - /tmp/test-etcd/etcd &
-   - go test -v -i $(go list ./... | grep -v '/vendor/')
-   - go test -v $(go list ./... | grep -v '/vendor/')
+   - go test -v -i $(go list ./... | grep -v '/vendor/' | grep -v 'examples/go')
+   - go test -v $(go list ./... | grep -v '/vendor/' | grep -v 'examples/go')