Get a ValueRef pointing to the function named *name*.
        NameError is raised if the symbol isn't found.

def get_function(self, name):
        """
        Get a ValueRef pointing to the function named *name*.
        NameError is raised if the symbol isn't found.
        """
        p = ffi.lib.LLVMPY_GetNamedFunction(self, _encode_string(name))
        if not p:
            raise NameError(name)
        return ValueRef(p, 'function', dict(module=self))