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.

examples/go/build.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+FISSION_PATH="github.com/fission/fission"
+
+docker run --rm -v $GOPATH/src/$FISSION_PATH:/usr/src/$FISSION_PATH \
+       -e GOPATH=/usr/ \
+       -w /usr/src/$FISSION_PATH/examples/go \
+       golang:1.8 go build -buildmode=plugin -o hello.so hello.go