some details in filtered simplicial complexes

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- some pep8 changes
- fix details in documentation


CC:  @jhpalmieri

Component: **algebraic topology**

Author: **Frédéric Chapoton**

Branch/Commit: **[`71cc4e9`](https://github.com/sagemath/sagetrac-mirror/commit/71cc4e960313234d61cd58ef57eec73f6b3e87b6)**

Reviewer: **John Palmieri**

_Issue created by migration from https://trac.sagemath.org/ticket/34759_

