Clean up notation around Vinnicombe metric in Ch 14 [robperf]

[Richard Murray]

The notation for the subsection on the Vinnicombe metric in Ch 14 is a bit confusing since we currently write P*(s) for P(-s), which could lead to confusion with the complex conjugate. Karl was going to think about whether there was a better notation that we could use and clean up this text.

[Richard Murray]

These were fixed up in commits 65ab88b and 7d92db3.

[Richard Murray]

Fixed.