tang: Add package into tree

tang: Add package into tree

Tang is lightweight server for binding data to network presence.
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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>