Ranges

Adds signed std::ssize() alongside unsigned size().

Ranges design cleanup before shipping (CPO naming, subrange adjustments).

Adds take_while, drop, drop_while, elements, keys, values and istream views.

Allows move-only single-pass iterators.

Requires contiguous iterators to support std::to_address.

Specifies iterator difference types wide enough to avoid overflow (integer-class types).

Specifies the size types of views.

Makes basic_istream_view::iterator non-copyable.

Allows move-only views.

Relaxes the over-constrained ranges comparison algorithms.

Makes range adaptors work with non-copyable iterators.

Replaces forwarding-range with the borrowed_range opt-in.

Constrains readable (now indirectly_readable) types properly.

Adds ranges versions of the newer algorithms (for_each_n, sample, clamp…).

Avoids template bloat by making take/drop on subrange-like views return the same view type.

Adds ranges::ssize.

Gives elements_view its own sentinel.

Fixes issues with the range access customization point objects.