fix some typos

[ocefpaf]

We cannot run codespell cleanly on notebooks yet but we can do:

for nb in **/*.ipynb ; do echo "${nb}"; cat "${nb}" | jupytext --from ipynb --to py:percent | codespell -; done 2>&1 | tee log

to convert with jupytext and run on the result.

[review-notebook-app]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

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[ocefpaf]

@MathewBiddle I'm inclined to remove the reviewnb now that GH rolled out the notebook diffs. This one look gorgeous BTW

[ocefpaf]

BTW, I cannot remove nbreview, not enough rights to the repo, but if you agree you can follow this to remove it:

[MathewBiddle]

Review Notebook App uninstalled. Should be removed in a bit.