Improve port naming of basic gates

[mkorbel1]

Motivation

Many of the gates have input port names like a and b and output ports like y. It would be great to name these something better.

Desired solution

Rename the ports to something better. For example, out is better than y.

Additional details

Many of these port names are not typically used by ROHD users since gates are accessed via overloaded operators. The Mux is one place where y is often visibly used.