Python documentation not exposed at top level

Our doc tools create some output html that describes the Python API, for example classwiredtiger_1_1_cursor.html . However, it doesn't appear that this can be found from the top level index.html.

If we want to have Python documentation, we should review these pages (I've looked at a few - at first glance they seem roughly correct - though there are some C-isms, and examples are in C), and make some sort of top level link.

Also, there is a pyfilter script (that uses a subordinate fixlinks.py) that is referenced by Doxygen.  These are both currently unused.  At one time, I think they were used to parse wiredtiger.py, and became unused when wiredtiger.py was renamed to be wiredtiger/_init_.py.  Part of WT-4711 restored the status quo of not using pyfilter and fixlinks.py, since this broke the build and introduced some differences in output. If we're going to support Python doc, this should be investigated. Otherwise we can remove these files.