Don't require an Encoder type while constructing FramedWrite so we can be generic over the lifetime

[w4]

PR Type

Feature/Bug Fix

PR Checklist

Check your PR fulfills the following:

• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• A changelog entry has been made for the appropriate packages.
• Format code with the latest stable rustfmt

Overview

This is a breaking change as it changes the signature of FramedWrite. This punts the responsibility of grabbing the type of item to write() rather than upon construction, essentially allowing us to treat the item as:

impl FramedWrite {
    fn write<'a>(&mut self, item: Item<'a>);
}

rather than the current:

impl<'a> FramedWrite<'a> {
    fn write(&mut self, item: Item<'a>);
}

---

The new signature of FramedWrite is now:

FramedWrite<WriteHalf<TcpStream>, MyEncoder, <MyEncoder as Encoder<MyType>>::Error>

rather than:

FramedWrite<MyType, WriteHalf<TcpStream>, MyEncoder>