Move contents of builtins/* to stdlib/*. This simplifies finding stubs.

stdlib/3/pwd.pyi

@@ -0,0 +1,18 @@
+# Stubs for pwd
+
+# NOTE: These are incomplete!
+
+import typing
+
+class struct_passwd:
+    # TODO use namedtuple
+    pw_name = ...  # type: str
+    pw_passwd = ...  # type: str
+    pw_uid = 0
+    pw_gid = 0
+    pw_gecos = ...  # type: str
+    pw_dir = ...  # type: str
+    pw_shell = ...  # type: str
+
+def getpwuid(uid: int) -> struct_passwd: ...
+def getpwnam(name: str) -> struct_passwd: ...