code: func encapHeaders(hdr http.Header) {
  	for k, vs := range hdr {
  		if k == "Content-Type" || strings.HasPrefix(k, "Fn-Http-H-") {
  			continue // we've passed this one
  		}
  
  		// remove them all to add them all back
  		hdr.Del(k)
  
  		// prepend this guy, add it back
  		k = "Fn-Http-H-" + k
  		hdr[k] = vs
  	}
  }
docs: // encapHeaders modifies headers in place per http gateway protocol