Do a pass for unwanted characters

[ctrueden]

I already looked quite a bit for characters that would be better represented in a different way. The following command is what I'm currently using to list what's still questionable there:

git grep -P -n "[^\x00-\x7F αβλχΔΠπτΨ∑σµμ ©® ° ⁰¹²³⁵⁶⁷₁₂≥≈≠≤≥±−×÷√≪≫∗★ ←→↓↑↩︎ †§ ÄÈÁÉÍÓÚČŠàèáćéíóúýãñäëïöüůêôčěňřšžßç 😁 ⌥⌘⏎ –—─│┌┐└┘├█″′«»]"

However, even some of the characters used above may be best changed for easier editing. In particular, the math symbols can become MathJax.

Another aspect of this is dashes: - – — ─. Maybe we should either: A) allow Markdown to convert things like -- to better dashes (does it?), or B) use – and — as appropriate.