All view types in Boost.URL have iterators that store raw pointers
to external data rather than references to the view object itself.
This means iterators remain valid even after the view is destroyed,
satisfying the borrowed_range requirements.
Specializations added for:
- decode_view, pct_string_view
- params_view, params_ref, params_encoded_view, params_encoded_ref
- segments_view, segments_ref, segments_encoded_view, segments_encoded_ref
fix#927
Alan de Freitas