- Fork this from the abandoned "weakref" PECL to provide WeakMap for php 7.0-7.4 and WeakReference for php 7.0-7.3
- Fix compilation errors for WeakMap in php 7.4
- Rename WeakRef to WeakReference to act as a polyfill for WeakReference in php before php 7.4.
- Make WeakReference constructor throw and require the use of WeakReference::create, like php 7.4
- Fix edge cases when destructor of an old value modifies the weakmap during an update.
- Strictly prevent the creation of dynamic properties on a WeakReference.