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This replaces the current `all_of_t<Pred, Ts...>` with `all_of<Ts...>`,
with previous use of `all_of_t<Pred, Ts...>` becoming
`all_of<Pred<Ts>...>` (and similarly for `any_of_t`).  It also adds a
`none_of<Ts...>`, a shortcut for `negation<any_of<Ts...>>`.

This allows `all_of` and `any_of` to be used a bit more flexible, e.g.
in cases where several predicates need to be tested for the same type
instead of the same predicate for multiple types.

This commit replaces the implementation with a more efficient version
for non-MSVC.  For MSVC, this changes the workaround to use the
built-in, recursive std::conjunction/std::disjunction instead.

This also removes the `count_t` since `any_of_t` and `all_of_t` were the
only things using it.

This commit also rearranges some of the future std imports to use actual
`std` implementations for C++14/17 features when under the appropriate
compiler mode, as we were already doing for a few things (like
index_sequence).  Most of these aren't saving much (the implementation
for enable_if_t, for example, is trivial), but I think it makes the
intention of the code instantly clear.  It also enables MSVC's native
std::index_sequence support.