1.1.0: Add implementation for spl_object_id for PHP <= 7.1 by default

spl_object_id will be built into PHP as of PHP 7.2.
This alias should speed up code that would otherwise use PHP polyfills.
Add --enable-runkit-spl_object_id=no to disable the new function alias.

1.0.6: Initial release, based on the runkit7/runkit7 repo

This implements runkit_object_id() : ?int, which returns the object handle id if an object is passed in, and null if a non-object is passed in.