generatorset: move iteration code into _iterator _iterator handles the generator iteration. The `__iter__` method will need changes to handle ordering-related information.

generatorset: stop using a base as the _genlist It does not add anything and makes it more complicated to have a simple baseset implementation.

generatorset: drop the leading underscore in the class name This is a real smart set now.

generatorset: update the docstring now that it is a smartset The documentation was still stating that this class was not a smartset. We drop that part.

addset: drop the leading underscore from the class name This class is now a real smartset.

addset: this is a smartset, update the docstring The documentation was still stating that this class is a not a smartset. We drop that part.

addset: use the ascending argument in _iterordered Fix a bug where fastasc and fastdesc were iterator in the same order as self._ascending.

rebase: add help examples

rebase: attempt to clarify --base

manifest: rearrange add() method and add comments for clarity Omit the check of bool(p1) since it's always true in practice: it will either be nullid or some valid manifest sha, and we know nullid won't ever be in the cache so we can simplify understanding of this code.