Rename the xmpp-parsers directory to parsers

This doesn’t change anything to the name of the crate, just makes
autocompletion easier by not sharing the same prefix as the xmpp crate.

xmpp-parsers/src/util/mod.rs

@@ -1,15 +0,0 @@
-// Copyright (c) 2019 Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
-//
-// This Source Code Form is subject to the terms of the Mozilla Public
-// License, v. 2.0. If a copy of the MPL was not distributed with this
-// file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
-/// Error type returned by every parser on failure.
-pub mod error;
-
-/// Various helpers.
-pub(crate) mod helpers;
-
-/// Helper macros to parse and serialise more easily.
-#[macro_use]
-mod macros;