QDoc: extend "\include" usage model to "\overload"s

It would be great if \include-ed text paragraphs would also be auto-added to function overloads (marked with \overload).

There are, obviously, certain pitfalls / exceptions:

• If \include contains argument (marked with \a) and overload does not have this argument, such auto-include is somewhat useless (although, such things are not generalized to be \include-d in the first place, I guess)
• There are very simple overloads that only contain \overload statement and that's it. For these, auto-include does not give much, the user is natively expected to see the descriptive version of a function. Let's call such documented functions "empty"

For me, as a user, QDoc is a complete black-box, so the following logic is just how a user would see it (no clue if certain stuff is possible to achieve at all or not):
1) It would be great if trivial (but not "empty") \overload-s would support auto-inclusion feature
2) for anything non-trivial, reporting a warning (e.g. "auto-inclusion is not possible") or anything similar is good enough, I guess
3) "empty" overloads are just ignored (see reasoning above)