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.

fission/function.go

@@ -74,7 +74,10 @@ func fnCreate(c *cli.Context) error {
 
 	fileName := c.String("code")
 	if len(fileName) == 0 {
-		fatal("Need --code argument.")
+		fileName = c.String("package")
+		if len(fileName) == 0 {
+			fatal("Need --code or --package argument.")
+		}
 	}
 
 	code := fnFetchCode(fileName)