Allow `<AddInName>_IntelliSense` folder to search for `...IntelliSense.xml` files

[Mo-Gul]

Maybe instead in allowing XInclude (see issue #81) you could allow a (sub)folder <AddInName>_IntelliSense in which several .IntelliSense.xml files can be stored to allow e.g. having one XML file per module in the AddIn.

The only problem I see so far is, what happens if there is both, the <AddInName>.IntelliSense.xml file and the <AddInName>_IntelliSense folder. Give one of them priority or try to load both?

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My goal is to use the XML files for IntelliSense as well as to use it to register the functions (i.e. use the content of the XML file for Application.MacroOptions).

Of course I am willing to share the result. There is already a working prototype. After I have added some unit tests (in VBA with the help of the awesome Rubberduck AddIn I could contact you, so you can have a look, if you are interested. If yes, how do you prefer that I contact you?