Added file format selection functionality to writer implementations.
Refactored the writer wrapper classes and related functionality to better support the above change and writers/backends with only one supported file format.
Added the detail::is_offset_view<> metafunction.
Added a missing formatted_image<>::subview_for_offset<>() overload.
Fixed the formatted_image<>::convert_to_prepared_view_worker<>() member function.
Added the new accumulate_greater() utility member function to the cumulative_result class.
Fixed the LibTIFF backend format construction/deduction code.
Fixed the libtiff_image::generic_convert_to_prepared_view<>() member function.
Removed commented out code.
Added missing include directives.
Removed some no longer necessary debugging code.
Minor other refactoring and stylistic changes.
