Deprecate Ice 3.3 and note its removal for 5.1

- Backport documentation fixes from 5.1 (use current doc links)
- Examples are based on Ice 3.5
- Ice 3.5 will work on Windows from 5.0.2 onward, so remove comments saying otherwise
- Ice 3.3 support is deprecated in 5.0 and will be removed in 5.1

--rebased-from #760