• Allow IO::Async::Stream to define custom reader/writer methods
  
• Support writeready-for-read and readready-for-write in Stream
  
• Allow Stream->write() on_write and write_len args
  
• Neatened and documented Future ->fail arguments and conventions
  
• Added Stream onwriteable{start,stop} events
  
• Added Handle->socket, ->bind and ->connect methods
  
• Revamp of Loop->connect logic; allow passing through an
  IO::Async::Handle instance