C++ thread API like native_handle

[ovanes]

I think it'd be great to have instead of operator void*() to have native_handle() as in thread API:

http://en.cppreference.com/w/cpp/thread/thread/native_handle

I would like to go consequently about usage of auto, but not having a function here causes either to cast, use explicit type void* or to call the context.operator void*().