Extended union types in C++11

This C++ library explores advanced definitions of union-types, using C++11 features. As such, your compiler (and standard library) needs to be set to run in C++11 mode. The library has (so far):

• super_union, a union that has its variant member types listed as template parameters. You can ignore having to recall the name (or name path) for each variant member and just address them by type. There is an option to address them via type index.
• tagged_union, a union that works like super_union except it also keeps track of which variant member is current. Addressing members must be done through the custom access functions.
• variant_size and variant_element, analogs to the meta-functions std::tuple_size and std::tuple_element that support the std::tuple (and std::pair and std::array) class templates. These class templates are specialized for the provided advanced union types in this library, and should be specialized for any union-like types you make.

The format of the library is like a prototype Boost library submission, which it may become. As such, the code is under the Boost license.