Better output for skipped instructions

[sbergen]

For cases where steps are executed conditionally, instead of using Return or Do with an empty body, it would be better to explicitly mark something as skipped (both for code and output clarity).

One option would be to use a Skip instruction e.g.

ContinueWith(x => x
    ? DoY()
    : Skip("Skipping Y because foo"))

Adding some kind of conditional operator is probably not a good idea, as it would then not support e.g. switch statements, and we don't want to reinvent control flow (any more than is necessary 😆).