tang: Update to version 7

Added License information.

Cleaned up Makefile for consistency between packages.

Added numerical prefixes to the patches for clarity.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

utils/tang/patches/030-readlink.patch

@@ -0,0 +1,13 @@
+--- a/src/tangd-update
++++ b/src/tangd-update
+@@ -33,8 +33,8 @@ fi
+ 
+ [ ! -d "$2" ] && mkdir -p -m 0700 "$2"
+ 
+-src=`realpath "$1"`
+-dst=`realpath "$2"`
++src=`readlink -f "$1"`
++dst=`readlink -f "$2"`
+ 
+ payl=()
+ sign=()