index_tuple_catを書いた

typename index_tuple_cat<index_tuple<Indices1...>, index_tuple<Indices2...>, ..., index_tuple<IndicesN...>>::typeがindex_tuple<Indices1..., Indices2..., ..., IndicesN...>となるようなメタ関数を書きました。

https://github.com/fimbul/shiro/blob/master/shiro/utility/index_tuple_cat.hpp