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

[bluss]

• [x] .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
• [x] .step() #133 -- when Iterator::step_by stabilizes rust-lang/rust/issues/27741 Rust 1.28 Deprecated in 0.8
• [x] .fold_while() when Iterator::try_fold is stable Rust 1.27 Deprecated in 0.8
• [x] repeat_call when repeat_with is stable rust-lang/rust/pull/48156 Rust 1.28 Deprecated in 0.8
• [x] .flatten() when Iterator::flatten is stable #262 Rust 1.29 Removed in 0.8
• [ ] unfold() when std::iter::unfold is stable rust-lang/rust/issues/55977

[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?