document support for Python 3.9 to 3.13

improve error management; shunt .run() with string to .eval()

emergency fix for handling errors, exposed by lmfit

Procedures: move 'build signature' to _signature() method, use in repr

more work to make exception messages more Python like

update doc to describe audit by IBM security research group

update docs

update rendered doc to include PDF and zipped html

remove date tag, unused decsciption from __init__.py

v 0.9.31