Adds a simple SocketHandler

I found myself needing a TCP GELF handler (IP address is used as access control, too easily forged in UDP and I can't setup RabbitMQ in this environment).

I'm not sure if it's that useful to include in the repository, since you probably should use UDP or the RabbitMQ handler in almost all situations and this can easily be dropped into your project, only importing `make_message_dict` from graypy.