input/rewind: move sources out of the "plugins" directory

This is not a plugin.

src/input/RewindInputStream.hxx

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2003-2017 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+/** \file
+ *
+ * A wrapper for an input_stream object which allows cheap buffered
+ * rewinding.  This is useful while detecting the stream codec (let
+ * each decoder plugin peek a portion from the stream).
+ */
+
+#ifndef MPD_REWIND_INPUT_STREAM_HXX
+#define MPD_REWIND_INPUT_STREAM_HXX
+
+#include "check.h"
+#include "Ptr.hxx"
+
+InputStreamPtr
+input_rewind_open(InputStreamPtr is);
+
+#endif