make closeOnEnd = true the default, add tests, and document

It was surprising to see closeOnEnd, and that it defaulted to false.
defaulting to true is more useful, and matched the behaviour of node's net module.

The problem is that pull streams work much better with streams that support half open mode.
see node docs: http://nodejs.org/api/net.html#net_net_createserver_options_connectionlistener

To get a protocol that needs half open mode to work with a stream that doesn't provide it I have this module:
https://github.com/dominictarr/pull-goodbye

Note that you need to wrap the application protocol, and not the network socket.
This is better, because the app is under your control, but the user should attach you to the network socket.

Since the pull request changes the default for `closeOnEnd`, this is a breaking change.