Merge pull request #7 from stoewer/metadata

Bindings for section and some copyright stuff

Welcome to 2014! ;-)
transmorgify: generic option_transmogrify

option_transmogrify should now work for all boost::optional<T>
tested with std::string and nix::Section
PySection: properties 'parent' and 'link'

parent and link return None if not set
link accepts None and Section as value