ddns-scripts: Update to Version 2.1.0-1 see description

- fixed postinst and prerm in Makefile
- implementation of provider specific update scripts into services and
services_ipv6 file.
	first Provider "no-ip.com"	- Thanks to DarkStarXxX for
request and testing
- finished uci/ddns wiki at http://wiki.openwrt.org/doc/uci/ddns
- rewritten retry management
- rewritten logging including following Issue 469
	https://github.com/openwrt/packages/issues/469
- stop running sections on hotplug ifdown event (like start on ifup)
- implement trap detection
	also kill "sleep" child processes
	SIGHUP to reload configuration (not really reloading, simply
starting a new process)
	/etc/init.d/ddns reload implemented
- code optimization
- new provider LoopiaDNS.se	Issue 494
	https://github.com/openwrt/packages/issues/494

Signed-off-by: Christian Schoenebeck <christian.schoenebeck@gmail.com>
Merge pull request #522 from chris5560/master

ddns-scripts: Update to Version 2.1.0-1 see description