readline: re-add the Interface#close() method; rename "end" to "close"

The idea here is to reduce the number of times that `setRawMode()` is called
on the `input` stream, since it is expensive, and simply pause()/resume()
should not call it.

So now `setRawMode()` only gets called at the beginning of the Interface
instance, and then when `Interface#close()` is called.

Test case included.