features for display and visuals

[owainevans]

1. TODO in 5a time inconsistency. redo exponential vs. hyperbolic graph in python.
2. how to get numbered lists with regular numerals (not roman numerals)?
3. there should be a default footer with a heading for endnotes (see example in 5a), a heading for references, and then links to previous chapter, next chapter and contents.
4. contents page should have "section header" (no link) and then each chapter in section. instead of current thing where section header is linked.
5. some codeboxes should have an extra button: "sample" which presses run continually (with some default time delay)