weakref: Add basic stub function to aid in porting.

Signed-off-by: Andrew Leech <andrew@alelec.net>

python-stdlib/weakref/manifest.py

@@ -0,0 +1,3 @@
+metadata(version="0.0.1")
+
+module("weakref.py")

python-stdlib/weakref/weakref.py

@@ -0,0 +1,11 @@
+"""
+# weakref
+https://docs.python.org/3/library/weakref.html
+
+Micropython does not have support for weakref in the VM, so currently this is a simple stub
+module that directly assigns the object reference to simplify porting of other libraries.
+"""
+
+
+def ref(obj):
+    return lambda: obj