Fix doxygen warnings
Fix the doxygen only.
Remove unused code
Properly recognize the constructor if we are given its alternate name

I.e a constructor can now be found with the 'real' name of the class
(fully desugared and expanded) or the alternate name we hold (indirectly)
in the fType.
Properly do function exact match when the argument are references.
Fix typos
Do not instantiate template ctors to make it take an ioctortype arg.

Fixes ROOT-5547.
Revert "Do not instantiate template ctors to make it take an ioctortype arg."

This reverts commit 223f631d327cd08540263c985d127cebc3255f9f.
Philippe and I violently disagree on whether template <typename T> Klass(T) should be taken into account when matching the RootIOCtor type.
I find this intricate, close to random (because it depends on what rootcling sees or whether the instantiation has been moved to a source file), non-obvious for such an explicit request.
Philippe finds it handy to invade / kidnap "unintrusively" existing templated c'tor signatures.
I request an explicit c'tor overload.
Philippe thinks that's too much of a requirement; he could not find a use case for the templated c'tor, though.
increase default xml buffer size to avoid frequent problesm with that.. sorry, don't know yet how to make that easily more flexible
Add a way to directly detect Constructor and Destructor (and convertor)

Add TFunction::ExtraProperty (and TClingMethodInfo::ExtraProperty)
and the enum values:
   kIsConstructor
   kIsConversion
   kIsDestructor

[The set of values use for Property, see TDictionery EProperty
uses all 32 bits of the typical enum underlying storage]