Update jaraco.windows to v3.6:

Dependencies:
* backports.functools-lru-cache	1.2.1
* jaraco.classes	1.3
* jaraco.collections	1.3.2
* jaraco.functools	1.11
* jaraco.structures	1.0
* jaraco.text	1.7
* jaraco.ui	1.4
* jaraco.windows	3.6
* more-itertools	2.2
* path.py	8.2.1
* six	1.10.0

libs/jaraco/classes/meta.py

@@ -0,0 +1,40 @@
+"""
+meta.py
+
+Some useful metaclasses.
+"""
+
+from __future__ import unicode_literals
+
+class LeafClassesMeta(type):
+	"""
+	A metaclass for classes that keeps track of all of them that
+	aren't base classes.
+	"""
+
+	_leaf_classes = set()
+
+	def __init__(cls, name, bases, attrs):
+		if not hasattr(cls, '_leaf_classes'):
+			cls._leaf_classes = set()
+		leaf_classes = getattr(cls, '_leaf_classes')
+		leaf_classes.add(cls)
+		# remove any base classes
+		leaf_classes -= set(bases)
+
+
+class TagRegistered(type):
+	"""
+	As classes of this metaclass are created, they keep a registry in the
+	base class of all classes by a class attribute, indicated by attr_name.
+	"""
+	attr_name = 'tag'
+
+	def __init__(cls, name, bases, namespace):
+		super(TagRegistered, cls).__init__(name, bases, namespace)
+		if not hasattr(cls, '_registry'):
+			cls._registry = {}
+		meta = cls.__class__
+		attr = getattr(cls, meta.attr_name, None)
+		if attr:
+			cls._registry[attr] = cls