Fix example and documentation rendering

[simon-perriard]

List of changes:

• fixed the example in the documentation of starky/lib.rs and make it runnable
• bumped katex version to the latest available (v0.16.11)
• added config.toml in the different .cargo to automate KaTeX rendering
• updated README
• tentatively added --no-deps flag for documentation rendering on https://docs.rs/, honestly don't know if it will work. Hopefully will render with KaTeX and fix the math rendering of pages like https://docs.rs/plonky2/latest/plonky2/gates/coset_interpolation/struct.CosetInterpolationGate.html

[Nashtare]

Thank you @simon-perriard for addressing this, and apologies for the delay. I've verified the display, and the rendering for the CosetInterpolationGate indeed looks much better, thanks!