Improve stream handling

[Renegade334]

• Closing any one of {socket stream, read stream, write stream} will result in the other two streams being closed as well.
• References to closed streams are removed from the Connection instance.
• Closing the read or write stream now calls $stream->end() rather than $stream->close() so that the send buffer is flushed first. (ref: #32)
• The closure returned by Client::getEndCallback() is now only called when the socket stream is closed. The 'end' event listeners for the read and write streams now simply call $stream->end().
• The prototype for Client::getEndCallback() has changed. It now takes the read and write stream instances as parameters, not the socket stream instance.

Unit tests are OK, but needs functional testing.

[coveralls]

Coverage remained the same at 99.06% when pulling e02ffc3d1f0034cdab4a518da26ac79da4509d76 on Renegade334:devel-stream-handling into 96462eaf6a6cd9f6fe343bf5aac52dea9bc9c219 on phergie:master.

[coveralls]

Coverage remained the same at 99.06% when pulling e02ffc3d1f0034cdab4a518da26ac79da4509d76 on Renegade334:devel-stream-handling into 96462eaf6a6cd9f6fe343bf5aac52dea9bc9c219 on phergie:master.

[coveralls]

Coverage remained the same at 99.059% when pulling e02ffc3d1f0034cdab4a518da26ac79da4509d76 on Renegade334:devel-stream-handling into 96462eaf6a6cd9f6fe343bf5aac52dea9bc9c219 on phergie:master.

[elazar]

Thanks! :)