Decode calculator string representation

Ensure that when the calculator is printed as a string, an actual string
is returned and not a bytes literal.
Add connect() method for convenience

Implement a connect() method. When this method is called, CyTI simply
connects to the first calculator it finds and returns the resulting
Calculator. This is especially useful when using CyTI in the REPL and
you only have one calculator connected to your computer. Actual scripts,
of course, should generally prefer using find_connections().
Update README example

Update the example in the README to use the connect() function. This
helps to demonstrate the simplicity of using CyTI.