List marshaling and py3 bug fix

* Now using `items` instead of `iteritems` for iterating over dictionaries, as the latter is not supported in Py3
* UDF arguments can be marshalled as `"list"` so that rather than arriving as tuples or tuples of tuples, they arrive as lists or lists of lists.
* Now using `Application.PathSeparator` to calculate paths in the add-in, even though it shouldn't make any difference on any machine, for now.

Author: ericremoreynolds

addin/xlpython.xlam

@@ -55,7 +55,7 @@ def xlret(marshal=None, **kwargs):
 	def inner(f):
 		xlf = xlfunc(f).__xlfunc__
 		xlr = xlf["ret"]
-		for k, v in kwargs.iteritems():
+		for k, v in kwargs.items():
 			if k in xlretparams:
 				xlr[k] = v
 			else:
@@ -74,7 +74,7 @@ def inner(f):
 		if arg not in xlf["argmap"]:
 			raise Exception("Invalid argument name '" + arg + "'.")
 		xla = xlf["argmap"][arg]
-		for k, v in kwargs.iteritems():
+		for k, v in kwargs.items():
 			if k in xlargparams:
 				xla[k] = v
 			else:

addin/xlpython/__init__.py

@@ -131,7 +131,7 @@ def Var(self, obj, lax=False):
 		if lax:
 			t = type(value)
 			if t is dict:
-				value = tuple(value.iteritems())
+				value = tuple(value.items())
 			elif t.__name__ == 'ndarray' and t.__module__ == 'numpy':
 				value = value.tolist()
 		if type(value) is tuple: