Add class for config and strings.

Add class for config and strings.

Class Taion::Core::Config holds simple string-string dictionary. It loads data
from specified file which can be given as a path (filename contains slash) or
simple filename in which case it can be the current directory, /etc, /usr/etc
or /usr/local/etc.

Class Tairon::Core::String is just a warapper around std::string providing some
convinient methods. It can be rewritten to use implicit sharing in the future.