- Adds index_if
- Rewrites detail::index_if to use recursive alias stuff
optimized for tuple and basic_tuple
- find_if now uses index_if for Iterables
- at_key now uses index_if for Sequence
- Removes duplicate code and unnecessary special case implementations
- detail::advance_until
- at_key::advance_until
- tuple_tag implementation of find_if
- Uses Foldable instead of Sequence for cases where length is known.
(find_if had a specialization when Iterable and not Sequence)
- Adds test.*.auto.index_if for Sequences
- Adds test support/counter for testing infinite iterables
