Replace unicode chars that RST auto-substitutes

[abidingabi]

To check for unicode characters, one can run: find source/docs -name "*.rst" | xargs grep -P '[^\x00-\x7F]'

It may be prudent to remove the remaining unicode characters, but this commit only removes curly quotes, en/em-dashes, non-breaking spaces, and ellipses, for which RST has simple substitions from ASCII.

[abidingabi]

It also may be prudent to add a CI check for this in the future, it is cheap and unicode characters can easily sneak in if text is copied from e.g. Microsoft Word or Google Docs which do their own text substitutions.