~~Implement `AsyncSequence/split()` functions similar to
`String/split()` functions in std-lib.~~
Implement `AsyncSequence/splitLines()` functions similar to
`String/split(whereSeparator: \.isNewline)` in std-lib.
### Motivation:
~~Provide an easy way for users to split the data incoming from an async
sequence, using their preferred separator.~~
Provide an easy way for users to split the data incoming from an async
sequence, on new lines.
### Modifications:
Add `internal SplitMessageDecoder: NIOSingleStepByteToMessageDecoder`.
Add `public NIOSplitLinesMessageDecoder:
NIOSingleStepByteToMessageDecoder`.
Add `public
AsyncSequence/splitLines(omittingEmptySubsequences:maximumBufferSize) ->
AsyncSeq<ByteBuffer>`.
Add `public
AsyncSequence/splitUTF8Lines(omittingEmptySubsequences:maximumBufferSize)
-> AsyncSeq<String>`.
### Result:
Users can easily split the data.
