I will add again the inner_allocator_type.
Specialization of rtcpp::allocator for node types.
The class bst is now taking and allocator with parameter type T not node_type.

- Internally it rebinds to the appropriate allocator.
- Member functions of class node_stack have been renamed.
bst working working with std::allocator.
Merge branch 'master' of https://github.com/mzimbres/rtcpp