Add contributors to the License.txt file

LICENSE

-Copyright (c) 2006-2014 Andy Matuschak
-Copyright (c) 2013-2014 Kornel Lesinski
-Copyright (c) 2014 Petroules Corporation, Sparkle Project contributors
+© 2006-2013 Andy Matuschak
+© 2009-2013 Elgato Systems GmbH.
+© 2011-2014 Kornel Lesiński
+© 2014 C.W. Betts
+© 2014 Petroules Corporation, Sparkle Project contributors
+© 2014 Big Nerd Ranch
+All rights reserved.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of
 this software and associated documentation files (the "Software"), to deal in
@@ -23,10 +27,10 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 EXTERNAL LICENSES
 =================
 
-License for bsdiff.c and bspatch.c, from bsdiff 4.3 (<http://www.daemonology.net/bsdiff/>):
+bspatch.c and bsdiff.c, from bsdiff 4.3 <http://www.daemonology.net/bsdiff/>: © 2003-2005 Colin Percival.
+SUDSAVerifier.m: © 2011 Mark Hamlin.
 
-Copyright 2003-2005 Colin Percival
-All rights reserved
+All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted providing that the following conditions