add functionality becoming daemon process and use Boost.Asio

To become a daemon it is necessary to deal with async operations.
So decide to use Boost.Asio for networking and general async operations.
Also to get absolute path use Boost.filesystem.
INTERVAL to specify interval seconds added to config file variable.
mydns_updater.cpp: handle exceptions to re-invoke timer handler
support PKGBUILD
Merge branch 'daemon'

Now mydns_update can become a daemon.
Add support for PKGBUILD