Diferenças entre Boost.Coroutine e Boost.Coroutine2

Quais são as principais diferenças entreBoost.Coroutine [http://www.boost.org/doc/libs/1_61_0/libs/coroutine/doc/html/index.html]e Boost.Coroutine2 [http://www.boost.org/doc/libs/1_61_0/libs/coroutine2/doc/html/index.html] ?