icl/iterator.hpp and icl/detail/element_iterator.hpp include <boost/config/warning_disable.hpp>

`icl\iterator.hpp` and `icl\detail\element_iterator.hpp` include ``. This disabled the MSVC warning C4996 without re-enabling it again.

For context: C4996 is MSVC's warning for using deprecated stuff. This means code that uses Boost.Icl will not get warning C4996 which IMO is quite bad. `` even contains the following comment:
```
// IT SHOULD NOT BE INCLUDED BY ANY BOOST HEADER.
//
// YOU SHOULD NOT INCLUDE IT IF YOU CAN REASONABLY FIX THE WARNING.
```

Inspect icl/iterator.hpp and icl/detail/element_iterator.hpp, starting with their inclusion of boost/config/warning_disable.hpp and any surrounding warning pragmas. Check the headers with MSVC warning C4996 enabled, and confirm that Boost.Icl no longer suppresses the warning for downstream code without introducing warnings in these headers.

Written by the indexing model from the issue text.