Associated types of TryFuture and TryStream

[MajorBreakfast]

Currently we have:

pub trait Future { type Output; ... }
pub trait TryFuture { type Item; type Error; ... }

pub trait Stream { type Item; ... }
pub trait TryStream { type TryItem; type TryError; ... }

• TryStream's success associated type cannot be called Item because Stream already uses that name for its associated type. That's why we end up with the not so great names TryItem and TryError
• TryFuture and TryStream have inconsistently named associated types

Here's what I propose:

pub trait Future { type Output; ... }
pub trait TryFuture { type Ok; type Err; ... }

pub trait Stream { type Item; ... }
pub trait TryStream { type Ok; type Err; ... }

That way the naming would be consistent with the variants of the Result enum!

Future<Output = Result<T, E>>
TryFuture<Ok = T, Err = E>

Stream<Item = Result<T, E>>
TryStream<Ok = T, Err = E>

[MajorBreakfast]

Maybe Error instead of Err to align with the Try trait

[MajorBreakfast]

Implemented by #1094