Implemented net.Conn interface on websocket connection.

Hi grayburd,

When I use your websocket library,  having a wee bit of trouble in porting all functions from original TCP protocol.

And then, I implemented the net.Conn interface on your websocket connection.

The major modification is DO NOT return io.EOF when finished one message.  The error will cause the above codes to close the connection.

The best implementation is support net.Conn interface on websocket.Conn directly.

But it's hard to me to modify so much codes,  and I fear it will break the robustness of your codes.

OK, if you have any questions or suggestions please let me know.

Peihao@ShangHai