metomi/rose#311: tidy use of delimiters

This addresses #311.

<samp>trigger</samp> expressions do actually require semi-colons in the current formulation, but occasionally it may work with newlines as an accident. The ability to use newline delimited value lists may be useful.

On the other hand, semi-colons are not necessary for <samp>fail-if/warn-if</samp>, if expressions are newline-separated.

I've changed both the <samp>trigger</samp> and the <samp>fail-if/warn-if</samp> expression examples to always have semi-colons. This applies even for single expressions, and the last expression in a group - it's better style.