Natural sort

There is still no easy natural sort algorithm in Qt item models. It becomes really messy when sorting on a column and one ends up with:

1
100
1000
2
20
35
4

etc.

A solution based on QAbstractItemModel::sort() and Qt::SortOrder would be nice. An alternative solution for sorting would be:

myView->setNaturalSort(true);

Also, making the algorithm available somewhere else, e.g. QString, would allow its usage anywhere in an application, even outside item views.