Added support for optional explanation parameter to the \versionadded macro. Refactored do_cmd_versionadded() and do_cmd_versionchanged() to do most of the work in a helper function, with the do_cmd_*() wrappers just supplying a portion of the replacement text.

\chapter{Python Runtime Services
         \label{python}}

The modules described in this chapter provide a wide range of services
related to the Python interpreter and its interaction with its
environment.  Here's an overview:

\localmoduletable