Moved code from future_then_base to future_state.
Added future_state::continue_with (for continuations, does not return a future).
Pretty much untested version of 'future<T> unwrap(future<future<T>>)'
Added header with forward declarations
Added type traits header with is_tuple and is_promise
Replaced future::poll() with future::ready() (N3428)
Shortcut for await when future is already 'ready'.
Added tag to private interfaces
unwrap is not a member function of future
Removed explicit qualifiers
Added make_future
For now ltl::future is like std::shared_future, makes many things simpler
Untested when_all combinator (simple cases compile).
Resulting futures are not awaitable yet