Fixed bug in add-in which caused it to malfunction with workbooks with a space in the filename.
Merge branch 'master' of https://github.com/ericremoreynolds/excelpython
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.