Add a splice of ShortByteString builder #664

There is

shortByteString :: ShortByteString -> Builder

but sometimes we want to write only a part of a SBS, i.e.

partOfShortByteString :: Int {- ^ offset -} -> Int {- ^ length -} -> ShortByteString -> Builder

as there aren't efficient take and drop for SBS.

We can go one abstraction lower and provide:

byteArray :: ByteArray -> Builder
partOfByteArray :: nt {- ^ offset -} -> Int {- ^ length -} -> ByteArray -> Builder

as ByteArray is now "the" type, SBS is just a small wrapper around it.

If maintainers are happy with an idea, I'll make a PR.