Add support for logging over TCP

Rename LogstashHandler to TCPLogstashHandler, make it subclass
directly from logging.SocketHandler, and create a subclass,
UDPLogstashHandler, that inherits from DatagramHandler.

Also add LogstashHandler as an alias for UDPLogstashHandler for
backward compatibility.
s/TCP/UDP/ for the default
Merge pull request #7 from javawizard/master

Add support for logging over TCP