Allow to use EitherOrBoth<T> to mean the same as EitherOrBoth<T, T>

[glandium]

No description provided.

[phimuemue]

Hi there, thanks for the idea.

Honest question: Does this - apart from avoiding a repeated type - enable something that could not be done with EitherOrBoth as it stands now? (E.g. allow usage in some generic contexts?) Did you experience problems with it?

[glandium]

No, I was just trying to avoid the repeated type, which can be bothersome when it's long.

[jswrenn]

There are a few places in our tests that could take advantage of this change:

itertools/tests/merge_join.rs

Lines 59 to 98 in 0897f56

	let expected_result: Vec<EitherOrBoth<u32, u32>> = vec![
	EitherOrBoth::Right(1),
	EitherOrBoth::Right(2),
	EitherOrBoth::Right(3),
	EitherOrBoth::Left(4),
	EitherOrBoth::Left(5),
	EitherOrBoth::Left(6),
	];
	let actual_result = merge_join_by(left, right, |l, r| l.cmp(r)).collect::<Vec<_>>();
	assert_eq!(expected_result, actual_result);
	}
	#[test]
	fn interspersed_left_and_right() {
	let left: Vec<u32> = vec![1, 3, 5];
	let right: Vec<u32> = vec![2, 4, 6];
	let expected_result: Vec<EitherOrBoth<u32, u32>> = vec![
	EitherOrBoth::Left(1),
	EitherOrBoth::Right(2),
	EitherOrBoth::Left(3),
	EitherOrBoth::Right(4),
	EitherOrBoth::Left(5),
	EitherOrBoth::Right(6),
	];
	let actual_result = merge_join_by(left, right, |l, r| l.cmp(r)).collect::<Vec<_>>();
	assert_eq!(expected_result, actual_result);
	}
	#[test]
	fn overlapping_left_and_right() {
	let left: Vec<u32> = vec![1, 3, 4, 6];
	let right: Vec<u32> = vec![2, 3, 4, 5];
	let expected_result: Vec<EitherOrBoth<u32, u32>> = vec![
	EitherOrBoth::Left(1),
	EitherOrBoth::Right(2),
	EitherOrBoth::Both(3, 3),
	EitherOrBoth::Both(4, 4),
	EitherOrBoth::Right(5),
	EitherOrBoth::Left(6),
	];

Can you modify them accordingly?