Merge pull request #85 in ZP/z-push from bugfix/ZP-756-memory_get_peak_usage-is-not-available to develop

* commit '99ddef76':
  ZP-756 add compat function for memory_get_peak_usage.
  ZP-756 add compat function for memory_get_peak_usage.

(cherry picked from commit 7b3448b1)

Conflicts:
	src/lib/utils/compat.php