New Feature: Handling of internal QML properties/methods

In QML the (undocumented) convention to declare internal properties and methods is to have the name starting with double-underscore "__".

Currently, we need to add the /* \internal */ marker before all our internal types so they don't show up in the documentation.

It would be nice that the doc tool detects automatically those properties/methods as internal and thus doesn't include them in the doc without the need for the internal tag.