revset: add documentation and comment for _generatorset (clean up some old irrelevant comment in the process)

revset: add some documentation for lazyset

revset: added documentation and comment for spanset class

revset: extend sorting tests

merge with crew

revset: changed smartset methods to return ordered addsets Now when adding two structures that are ordered, they are wrapped into an _addset and they get added lazily while keeping the order.

revset: added isascending and isdescending methods to _addset This methods are intended to duck-type baseset, so we will still have _addset as a private class but now we can return it without wrapping it into an orderedlazyset or a lazyset. These were the last methods to add for smartset compatibility.

revset: added __add__ method to _addset This method is intended to duck-type baseset, so we will still have _addset as a private class but we will be able to return it without wrapping it into an orderedlazyset or a lazyset.

revset: added __sub__ mehtod to _addset This method is intended to duck-type baseset, so we will still have _addset as a private class but now will be able to return it without wrapping it into an orderedlazyset or a lazyset.

revset: added __and__ method to _addset This method is intended to duck-type baseset, so we will still have _addset as a private class but we will be able to return it without wrapping it into an orderedlazyset or a lazyset.

revset: added ascending and descending methods to _addset This methods are intended to duck-type baseset, so we will still have _addset as a private class but will be able return it without wrapping it into an orderedlazyset or a lazyset.

revset: added filter method to _addset This method is intended to duck-type baseset, so we will still have _addset as a private class but we will be able return it without wrapping it into an orderedlazyset or a lazyset.

revset: added comments to all methods needed to duck-type from baseset All this methods are required to duck-type for any class that works as a smart set.

revset: use more explicit argument names for baseset methods Use other instead of x and condition instead of l

revset: added isascending and isdescending methods to smartset classes This methods state if the class is sorted in an ascending or descending order We need this to implement methods based on order on smartset classes in order to be able to create new objects with a given order. We cannot just rely on a simple boolean since unordered set are neither ascending nor descending.