corresponding note to documentation. Patch by Ivan L.

Patch by Ammar Askar.

It got messed up when I merged my private 3.5.3 release
changes with new work happening in the 3.5 main branch.
(3.5 main branch was in "3.5.3rc1", my branch was "3.5.3+",
and Mercurial helpfully merged the two in a kind of nonsense way.)

Thanks to Evan_ for the report and patch.

* Indent versionchanged at method level, not class level
* Mark up ``--help`` to avoid generating an en dash
* Use forward slash in Unix command line with a dollar sign ($) prompt