png versions of path diagrams

[Phil Wood]

I had a request to convert the svg files in the Markdown files to png so people can use them in classes. I added these to the PDF table in the group. Myself I kind of thing keeping the svg files in Markdown is usefulb because it lets people edit the graphics for other purposes like Adobe Illustrator and such.

https://sites.google.com/view/understanding-structureal-equa/home

FYI

Phil