Implement C++11 variadic templates based fusion::vector.

Note: This implementation doesn't accept using of trailing void_ within
template parameter: it will break some backward compatibility.
Fixes that it couldn't store due to explicit ctor.
Remove dependencies of mpl::vector within c++11 fusion::vector

and ugly hack since Boost.MPL has no variadic templates based vector.
Adjust fusion::nview for variadic templates based fusion::vector

since FUSION_MAX_VECTOR_SIZE won't define in c++11.
Improve integer_sequence implementation.