Allow lshift to operate on any library. If only one name, return it, else None

masque/library.py

@@ -587,8 +587,13 @@ class MutableLibrary(Library, MutableMapping[str, 'Pattern'], metaclass=ABCMeta)
         self.add(tree.library, rename_theirs=rename_theirs)
         return name
 
-    def __lshift__(self, other: 'Tree') -> str:
-        return self.add_tree(other)
+    def __lshift__(self, other: Mapping[str, 'Pattern']) -> Optional[str]:
+        if isinstance(other, Tree):
+            return self.add_tree(other)     # Add library and return topcell name
+
+        name = next(other.keys()) if len(other) == 1 else None  # If only one name, return it
+        lib.add(other)
+        return name
 
     def dedup(
             self: ML,