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/files/tangdx

@@ -0,0 +1,12 @@
+service tangd
+{
+    port            = 8888
+    socket_type     = stream
+    wait            = no
+    user            = root
+    server          = /usr/libexec/tangdw
+    server_args     = /usr/share/tang/cache
+    log_on_success  += USERID
+    log_on_failure  += USERID
+    disable         = no
+}