Merge Phil Zimmermann's libzrtp as a FreeSWITCH library

Thanks to Phil Zimmermann for the code and for the license exception
we needed to include it.

There remains some build system integration work to be done before
this code will build properly in the FreeSWITCH tree.

libs/libzrtp/include/zrtp_version.h

@@ -0,0 +1,19 @@
+/*
+ * libZRTP SDK library, implements the ZRTP secure VoIP protocol.
+ * Copyright (c) 2006-2009 Philip R. Zimmermann.  All rights reserved.
+ * Contact: http://philzimmermann.com
+ * For licensing and other legal details, see the file zrtp_legal.c.
+ * 
+ * Viktor Krykun <v.krikun at zfoneproject.com> 
+ */
+
+#ifndef __ZRTP_VERSION_H__
+#define __ZRTP_VERSION_H__
+
+#define LIBZRTP_VERSION_MAJOR		1
+
+#define LIBZRTP_VERSION_MINOR		13
+#define LIBZRTP_VERSION_BUILD		604
+#define LIBZRTP_VERSION_STR			"v1.13 604"
+
+#endif /*__ZRTP_VERSION_H__*/