Update changelog for bytestring-0.12.2.0

[Bodigrim]

No description provided.

[clyring]

The existing entries and organization look good to me.

• Improve benchmarks for small Builders #680 also adds NFData instances for BufferRange and Buffer.
• instance IsList Builder #672 also changes fromListN in the IsList instance for StrictByteString.
  • Technically this is a breaking change as-is, since the use of packUptoLenBytes means that the input list will be truncated if the list is longer than the size hint suggests.
• instance IsList Builder #672 also moves toLazyByteString into Data.ByteString.Builder.Internal and exports it there.

Also, we are still only working around #665 in a Hackage revision. We should fix it properly (or at least merge the contents of the Hackage revision into the source repo) before cutting a release. I can prepare a MR for this tomorrow, if you don't beat me to it.

[Bodigrim]

Technically this is a breaking change as-is, since the use of packUptoLenBytes means that the input list will be truncated if the list is longer than the size hint suggests.

Yeah, maybe it's better to revert the change to instance IsList StrictByteString.

We should fix it properly (or at least merge the contents of the Hackage revision into the source repo)

Let's make our lives easier and just backport the revision.

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Feel free to push any corrections into this branch.