Various simple fixes

[fchapoton]

a sequence of commits fixing various things, mostly cosmetics

[oscarbenjamin]

Thanks. Did you use a tool to find these?

There was some recent discussion about cython-lint: #191 (comment).

It would be good to have some sort of linting for local use and for CI and I think that cython-lint at least picks up on some of the cases you have covered here. I just checked and this PR reduces the number of cython-lint complaints from 455 to 342.

There are no e.g. no W605 invalid escape sequence errors with the changes here so now it would be good to add a CI check that use cython-lint and checks for those.

[fchapoton]

I indeed used cython-lint. I can try to help make a linter with cython-lint in some other pull request, sure.

also used codespell to find typos and sage --tox -e rst to check the rst syntax

[oscarbenjamin]

sage --tox -e rst to check the rst syntax

Is that just something in-house for Sage?

I can try to help make a linter with cython-lint in some other pull request, sure.

Feel free to do that. I wasn't suggesting that you need to do it or that it needs to be part of this PR though. I was just observing that it is something that we should do generally speaking. First step of course is to fix existing errors as you have done here.

[oscarbenjamin]

Looks good. Thanks!