Errors in parapoly expansions should show context about the parameters and where they are used

[Beefster09]

Whenever I have issues with parapoly procedures, it's often a struggle to figure out what invocation is making it angry.

It would be helpful to know what the compile-time parameters are set for each case of the error. Ideally also the call sites, but since that list could be quite large, I could understand not showing anything or only showing a subset of the call sites.