Feature: Support unwrapping object streams by buffering original write chunks in array.
(#15 by @clue)

Feature: Clean up unneeded references for unwrapped streams when closing.
(#18 by @clue)

Fix: Writing to closed unwrapped stream should return false (backpressure).
(#17 by @clue)

Improve test suite to support PHPUnit 7, PHP 7.3 and fix incomplete test
and improve API documentation.
(#16 and #19 by @clue)