Inital work on Rust support (#333)

* Inital work on Rust support

* update accepted runtimes

* fn: fix rust build

* Last tweaks and README.md

* fix typo

* update comment on rust.go

fn/langs/base.go

@@ -13,6 +13,8 @@ func GetLangHelper(lang string) (LangHelper, error) {
 		return &RubyLangHelper{}, nil
 	case "python":
 		return &PythonHelper{}, nil
+	case "rust":
+		return &RustLangHelper{}, nil
 	}
 	return nil, fmt.Errorf("No language helper found for %v", lang)
 }