tang: Add package into tree

Tang is lightweight server for binding data to network presence.
---
Tang's source: https://github.com/latchset/tang

Maintainer: @Tiboris

Compile tested: (mips, TL-WR842N, 17.01.4, r3560-79f57e422d)

**Tang requires a few other software libraries:**

1. libhttp-parser
2. xinetd's socket activation
3. jose >= 8

**Two new files compared to tang upstream:**
- tangdx : configuration file for xinetd
- tangdw : wrapper for tangd service
	- puts timestamp when service activated, and
	- redirects stderr to log file in /var/log/

**Removed systemd requirement**

Signed-off-by: Tibor Dudlák <tdudlak@redhat.com>

utils/tang/patches/use-readlink-in-tangd-update.patch

@@ -0,0 +1,15 @@
+diff --git a/src/tangd-update b/src/tangd-update
+index 652dbef..01aa842 100755
+--- 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=()