Merge pull request #42 from tdi/master

Update headers not to mention LICENSE.txt but licenses directly Closes #31

src/hash.c

@@ -6,10 +6,7 @@
 **  This software is provided AS-IS with no warranty, either express
 **  or implied.
 **
-**  This software is distributed under license and may not be copied,
-**  modified or distributed except as expressly authorized under the
-**  terms of the license contained in the file LICENSE.txt in this
-**  distribution.
+**  This program is dual licensed under the MIT and GPLv3 licenses.
 */
 
 /** @file