- new pybind11::base<> attribute to indicate a subclass relationship
- unified infrastructure for parsing variadic arguments in class_ and cpp_function
- use 'handle' and 'object' more consistently everywhere
Using object class to hold converted object automatically deallocates
object if an exception is thrown or scope is left before constructing
complete Python object.
Additionally added method object::release() that allows to release
ownership of python object without decreasing its reference count.
