support allow_delete_body for protoc-gen-grpc-gateway

this fixes up #280

protoc-gen-grpc-gateway/main.go

@@ -25,6 +25,7 @@ import (
 var (
 	importPrefix      = flag.String("import_prefix", "", "prefix to be added to go package paths for imported proto files")
 	useRequestContext = flag.Bool("request_context", false, "determine whether to use http.Request's context or not")
+	allowDeleteBody   = flag.Bool("allow_delete_body", false, "unless set, HTTP DELETE methods may not have a body")
 )
 
 func parseReq(r io.Reader) (*plugin.CodeGeneratorRequest, error) {
@@ -77,6 +78,7 @@ func main() {
 	g := gengateway.New(reg, *useRequestContext)
 
 	reg.SetPrefix(*importPrefix)
+	reg.SetAllowDeleteBody(*allowDeleteBody)
 	if err := reg.Load(req); err != nil {
 		emitError(err)
 		return