The cutting block: These features will be removed from itertools eventually

[bluss]

• .foreach() -- when Iterator::for_each stabilizes and it's old enough so that the deprecation is not annoying. Introduced in Rust 1.21. Deprecated in 0.8
• .step() step() slowness #133 -- when Iterator::step_by stabilizes Tracking issue for step_by stabilization rust-lang/rust#27741 Rust 1.28 Deprecated in 0.8
• .fold_while() when Iterator::try_fold is stable Rust 1.27 Deprecated in 0.8
• repeat_call when repeat_with is stable Add std/core::iter::repeat_with rust-lang/rust#48156 Rust 1.28 Deprecated in 0.8
• .flatten() when Iterator::flatten is stable Deprecate flatten #262 Rust 1.29 Removed in 0.8
• unfold() when std::iter::unfold is stable Tracking issue for std::iter::from_fn rust-lang/rust#55977 Deprecated in 0.13

[Centril]

Everything in the list has been stabilized save for .flatten() which is getting stabilized atm.

[flxo]

Looks like .flatten() hit stable with 1.29.

[DevinR528]

Seems like unfold was merged in as from_fn, issue may now be close-able?