Sliced interface for ShortByteString

I think we could take some inspiration from [byteslice](https://hackage.haskell.org/package/byteslice). This would also address https://github.com/haskell/bytestring/issues/193, by expanding the api for `ByteArray` based types instead of changing `ByteString` to use `ByteArray`.

The docs for `ShortByteString` say
> It is suitable for use as an internal representation for code that needs to keep many short strings in memory, but it should not be used as an interchange type. That is, it should not generally be used in public APIs.

Having a sliced `ShortByteString` would allow using a `ByteArray` based type in public APIs, similar to `ByteString`.