* The implementation has been refactored to avoid internal virtual calls at places where
the type of the segment involved is known at compile time. Also, segment lookup (the
process to get to the segment for U from typeid(U)) has been greatly sped up by means
of a std::type_info* cache. These two improvements result in a combined reduction of
around 25-30% in insertion times. There's an API breaking change though: no longer
is std::type_index used and const std::type_info &'s have to be directly provided
instead --this is likely to go unnoticed by those of you already using the lib.