v2.6.0

• Feature: Significantly improve memory consumption and performance by only passing resolver args
  to resolver and canceller if callback requires them. Also use static callbacks without
  binding to promise, clean up canceller function reference when they are no longer
  needed and hide resolver and canceller references from call stack on PHP 7+.
  (#113, #115, #116, #117, #118, #119 and #123 by @clue)

  These changes combined mean that rejecting promises with an Exception should
  no longer cause any internal circular references which could cause some unexpected
  memory growth in previous versions. By explicitly avoiding and explicitly
  cleaning up said references, we can avoid relying on PHP's circular garbage collector
  to kick in which significantly improves performance when rejecting many promises.

• Mark legacy progress support / notification API as deprecated
  (#112 by @clue)

• Recommend rejecting promises by throwing an exception
  (#114 by @jsor)

• Improve documentation to properly instantiate LazyPromise
  (#121 by @holtkamp)

• Follower cancellation propagation was originally planned for this release
  but has been reverted for now and is planned for a future release.
  (#99 by @jsor and #122 by @clue)