Diagnose meaningless annotations

[Xazax-hun]

Diagnose when we annotate a non-pointer with gsl::lifetime, gsl::lifetime_out, gsl::lifetime_in.
Diagnose when we annotate a top-level pointer with gsl::lifetime_out.
Diagnose when we annotate a non-owner with gsl::lifetime_const.

Is there more ways to misuse annotations? Should we add these to the paper?

[mgehre]

We should be careful in a template context, where an annotation on T make sense/no-sense depending on whether T is a Owner, Pointer or otherwise.

[Xazax-hun]

Good point!