Set the _returncode attribute, so close() doesn't try to terminate the process.

Create the protocol on a separated line for readability and ease debugging.

...seEventLoop)

Ignore pipes for which the protocol is not set yet (still equal to None).

...is closed

Close the transport if the creation of the transport (if the waiter) gets an
exception.

Skip SSL tests on the ProactorEventLoop if ssl.MemoryIO is missing

Sort also imports in windows_utils.

StreamWriter now raises an exception if it is closed: write(), writelines(),
write_eof(), can_write_eof(), get_extra_info(), drain().

Don't call immediatly self._process_write_backlog() but schedule the call using
call_soon(). _on_handshake_complete() can be called indirectly from
_process_write_backlog(), and _process_write_backlog() is not reentrant.

transport at subprocess exit.
Clear also its reference to the transport.

Do nothing if the transport is already closed. Before it was not possible to
close the transport twice.

Check if the _sock attribute is None to check if the transport is closed.

Set the _read_fut attribute to None after cancelling it.
This change should fix a race condition with
_ProactorWritePipeTransport._pipe_closed().

* Use test_utils.run_briefly() to execute pending calls to really close
 transports
* sslproto: mock also _SSLPipe.shutdown(), it's need to close the transport
* pipe test: the test doesn't close explicitly the PipeHandle, so ignore
 the warning instead
* test_popen: use the context manager ("with p:") to explicitly close pipes

StreamWriter: close() now clears the reference to the transport
StreamWriter now raises an exception if it is closed: write(), writelines(),
write_eof(), can_write_eof(), get_extra_info(), drain().

Override the connect_read_pipe() method of the loop to mock immediatly
pause_reading() and resume_reading() methods.
The test failed randomly on FreeBSD 9 buildbot and on Windows using trollius.

Remove the exc variable, it's not used.

* Handle correctly CancelledError: just exit
* On error, log the exception and exit
Don't try to close the event loop, it is probably running and so it cannot be
closed.

...rojects
As per [their blog post of the 27th April](https://blog.readthedocs.com/securing-subdomains/) ‘Securing subdomains’:
> Starting today, Read the Docs will start hosting projects from subdomains on the domain readthedocs.io, instead of on readthedocs.org. This change addresses some security concerns around site cookies while hosting user generated data on the same domain as our dashboard.
Test Plan: Manually visited all the links I’ve modified.

From(proc.wait()) instead of form proc.wait()

Convert readthedocs link for their .org -> .io migration for hosted projects

Update also releaser URL

Be explicit about supporting only Python 2.7
Drop testing on appveyor because the needed dependencies no longer exist.
Incorporate #15 

Fixes #17 

Make socket.error with errno EBADF get raised as OSError.