improves specs for exception handling in Document.
improves specs for exception handling in Document.

We better avoid memoized helper methods in these examples, and also test that
warnings really appear on STDERR (while avoiding cluttering rspec output).

Improves #95

Sameer-Tilak/metainspector,jaimeiniesta/metainspector,jschwindt/metainspector,masarakki/metainspector,termscorpx/metainspector