Finish implementing Client.h

If you're willing to give up your custom IPAddress, and not overload connect function for UDP connections, we can implement the rest of Client.h. This makes your library code compatible with, and able to run examples from, Arduino Ethernet, Arduino WIfi, Spark Core, Pinoccio and many more TCP implementations that all support client.

Theres a bit of code duplication from the connectUDP I'd be happy to try to clean up if you had a preference how.

Thanks for considering!
Jacob