Some minor changes

• Added the $(WorkbookDir) macro for use in xlpython.cfg
• Added @xlsub decorator for defining user-defined subprocedures (as opposed to functions)
• Added vba keyword argument in @xlarg decorator, enabling you to hard-code argument values to a VBA expression evaluated at runtime - very useful for passing objects like Application or ThisWorkbook to the Python function
• COM objects are automatically wrapped using win32com.client.Dispatch when passed to Python so that they can be used dynamically without extra code.