fix EventLoopFuture.and's serious threading issues (apple#176)

Motivation:

EventLoopFuture.and had serious threading issues if the EventLoops
weren't the same.

Modifications:

Fixed the threading issues and tested them properly.

Result:

Hopefully `and` and `andAll` now don't crash if you use them across
EventLoops.

fix closed accepting Channels in closed ServerSocketChannels (apple#170)

Motivation:

For servers NIO had a race where when you start tearing down the
`ServerSocketChannel` and at roughly the same time a client connects, we
would not fully bring that channel up, nor tear it down. That lead to
open channels being deallocated which leads to a crash as that's an
illegal state.

Modifications:

Made sure newly accepted channels get closed if the
`ServerSocketChannel` is already clsing.

Result:

No crashes anymore when a client connects to a closing server.

Ensure channels don't get stuck completely unregistered. (apple#104)

Motivation:

It should be possible to have channels that are not registered
for any form of I/O without them getting stuck in that model
forever.

Modifications:

Remove the code that prevents channels registered for `.none` from
registering for anything else.

Result:

Channels can actually be registered for nothing without becoming
wedged open forever.

fix readme dependencies (apple#42)