Fix grammar summary in documentation

It didn't include the scrutinee itself.
Don't document equivalence of switch and a bare block

If a switch were equivalent to a bare block, then untargetted loop control
keywords (next/last/redo) within a case body would apply to the switch, not
any surrounding loop.  That would contradict the documentation, as well as
being undesirable.
Merge pull request #2 from arc/doc-fixes

Doc fixes