tuned: more antiquotations;

prefer host that is less likely to be down;

adapt and activate congprocs examples, following the current Simplifier implementation; minor tuning;

original Congproc_Ex.thy by Norbert Schirmer: still inactive;

provide Simplifier.set_mksimps_context (roughly following Norbert Schirmer): allow update of context when premises are added to the local simpset;

clarified signature;