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/README.md

@@ -0,0 +1,30 @@
+# Go examples
+
+The `go` runtime uses the [`plugin` package](https://golang.org/pkg/plugin/) to dynamically load an HTTP handler.
+
+## Requirements
+
+- go 1.8
+- A [go-runtime fission environment](environments/go/README.md)
+
+## Examples
+
+### hello.go
+
+`hello.go` is an very basic HTTP handler returning `"Hello, World!"`.
+
+
+```
+# Build the function as a plugin
+$ ./build.sh
+
+# Upload the function to fission
+$ fission function create --name hello --env go-runtime --package hello.so
+
+# Map /hello to the hello function
+$ fission route create --method GET --url /hello --function hello
+
+# Run the function
+$ curl http://$FISSION_ROUTER/hello
+Hello, World!
+```

examples/go/build.sh

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+#!/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

examples/go/hello.go

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+package main
+
+import (
+	"net/http"
+)
+
+func Handler(w http.ResponseWriter, r *http.Request) {
+	msg := "Hello, World!"
+	w.Write([]byte(msg))
+}