addset: offer a fastasc and fastdesc methods If the underlying object offers fast iterators, we use them to provide fast iterators too.

addset: split simple and ordered iteration We have two goals here. First, we would like to restore the former iteration order we had in 2.9. Second, we want this logic to be reusable for `fastasc` and `fastdesc` methods.

generatorset: promote to smartset This is not going to be efficient but we need all basic set classes to be smartsets for the other classes to work.

generatorset: implement __nonzero__ This is necessary to become a real smartset.

spanset: use base implementation for __add__

spanset: use base implementation for __sub__

spanset: use base implementation for __and__

spanset: use base implementation for filter

filteredset: use base implementation for filter

filteredset: use base implementation for __add__

filteredset: use base implementation for __sub__

filteredset: use base implementation for __and__

abstractsmartset: add default implementation for __sub__

abstractsmartset: add default implementation for __add__

abstractsmartset: add default implementation for __and__

abstractsmartset: add default implementation for filter

lazyset: rename the class to filteredset All smartsets try to be lazy. The purpose of this class is to apply a filter on another set. So we rename the class (and all its occurences) to `filteredset`.

lazyset: add order awareness to the class Just a bit of extra code makes the lazyset aware of order. This renders orderedlazyset useless. At some point, the `subset` will become responsible for this ordering logic. But we are not there yet because the various objects used as subsets are not good enough.

lazyset: remove min/max This is now handled by abstractsmartset.

baseset: remove min/max methods This is now handled by the base class.

abstractsmartset: add a default implementation for min and max This default implementation takes advantage of the fast iterator if available.

lazyset: drop now useless ascending/descending definition

lazyset: inherit the fastasc and fastdesc method from subset When the filtered subset has such methods, we can use them. It is implemented as properties to be able to quickly return None if no corresponding fastasc exists on the subset.

lazyset: split the iteration logic from the condition filtering logic So that the filter can be reused by `fastasc` or `fastdesc`.