0.3.0

• Stable release along with stable async/await!
• Added async/await to default features (#1953)
• Changed Spawn trait and FuturesUnordered::push to take &self (#1950)
• Moved Spawn and FutureObj out of futures-core and into `futures-task (#1925)
• Changed case convention for feature names (#1937)
• Added executor feature (#1949)
• Moved copy_into/copy_buf_into (#1948)
• Changed SinkExt::send_all to accept a TryStream (#1946)
• Removed ThreadPool::run (#1944)
• Changed to use our own definition of io::Cursor (#1943)
• Removed BufReader::poll_seek_relative (#1938)
• Changed skip to take a usize rather than u64 (#1931)
• Removed Stream impl for VecDeque (#1930)
• Renamed Peekable::peek to poll_peek (#1928)
• Added immutable iterators for FuturesUnordered (#1922)
• Made ThreadPool optional (#1910)
• Renamed oneshot::Sender::poll_cancel to poll_canceled (#1908)
• Added some missing Clone implementations
• Documentation fixes