Update docs generation for examples, add additional example

[Jekannadar]

The gen_example_pages.py script now separately handles Markdown, Source files, and images.
Examples are now expected to always be in a subfolder of examples in the root directory.

If there is a README.md present in a subfolder of examples:

• The H1 heading of the file becomes the name of the example folder in the docs.
• The README is named Overview in that doc folder.
• All Python files are moved into a subfolder Source Files, which replicates the source tree structure.

[codecov]

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