Remove segmented buffers

These classes is not used curretly.
Add byte array and ByteBuffer view for buffers
Fix static factory method

Factory methods for ArrayDecodeBuffer, ArrayEncodeBuffer,
ByteBufferDecodeBuffer is moved to Buffers.
Fix to be able to set attachment to Transport
Revert Decoder#readString(CharsetDecoder, int)
Add EncodeBufferGroup

Use to hold multiple EncodeBuffers in pipe line.