Initial stable release compatible with AMPHP v3 and fibers.

There are a number of renaming and compatibility breaks with 1.x versions:

• Added interface ResourceStream
• InputStream has been renamed to ReadableStream and now extends Amp\Closable. The read() method now supports an optional Cancellation parameter.
• OutputStream has been renamed to WritableStream and now extends Amp\Closable. WritableStream::end() no longer accepts an optional data chunk as parameter.
• IteratorStream has been repalced by ReadableIterableStream, which accepts any iterable of strings (particularly useful with Generator or Pipeline).
• ResourceInputStream has been renamed to ReadableResourceStream. The read() method has an additional, optional $limit parameter to specify the maximum number of bytes to read.
• ResourceOutputStream has been renamed to WritableResourceStream.
• InMemoryStream has been renamed to ReadableBuffer.
• OutputBuffer has been renamed to WritableBuffer.
• Payload now accepts a string in addition to a ReadableStream and is final now. Payload::buffer() may only be called once.
• Added a $limit param to Amp\ByteStream\buffer() and Payload::buffer() to set a limit on the maximum bytes that can be buffered.
• Added BufferedReader, a helper class for reading from ReadableStream using fixed lengths or delimiters found within the stream (#94)
• Added Pipe.
• Added StreamChannel implementing the Channel interface from amphp/sync.
• The zlib streams have been moved into the Compression sub-namespace and renamed to CompressingWritableStream and DecompressingReadableStream.
• Add CompressingReadableStream (#99)
• Add DecompressingWritableStream (#99)
• The base64 streams have been renamed to reflect the new interface names.
• InputStreamChain has been renamed to ReadableStreamChain.
• Renamed the $options param of parseLineDelimitedJson to $flags to match the json_decode function.