Rename `AsyncWrite::shutdown`

[carllerche]

Because this function is unrelated to TCP shutdown (and the AsyncWrite::shutdown impl for TcpStream does not call shutdown), the name of the function is very confusing.

A couple of options:

• finalize
• prepare_for_close
• poll_close_ready
• start_close

Related: #73.

[P-E-Meunier]

Cool. Why is shutdown for TcpStream not calling TCP shutdown?
Other than this, I'd vote for poll_close (why the _ready?). I find start_close confusing, given that one is expected to call it until it returns Async::Ready.

[carllerche]

@P-E-Meunier Because "AsyncWrite::shutdown" and TCP shutdown are two completely separate functions with different behaviors.

This is why AsyncWrite::shutdown needs to be renamed.

[carllerche]

The tokio-io crate has been moved into the tokio git repo.

I created a new issue over there. See link above.