Build system changes
--------------------
The minimum supported miniUPnPc API version is set to 10. This keeps compatibility with Ubuntu 16.04 LTS and Debian 8 `libminiupnpc-dev` packages. Please note, on Debian this package is still vulnerable to [CVE-2017-8798](https://security-tracker.debian.org/tracker/CVE-2017-8798) (in jessie only) and [CVE-2017-1000494](https://security-tracker.debian.org/tracker/CVE-2017-1000494) (both in jessie and in stretch).

Add release notes for 15993
doc: Add release notes for 15993
