LOAD CSV improvements (#887)

i think the first few (older) examples could be brought in line with the
newer examples i added

also, i'm pretty sure the tests will fail left and right - the expected
query results were written by hand ✋

finally, the GitHub diff is not really pretty ( = readable). there ought
to be a preview of the changes though

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Co-authored-by: Jessica Wright <[email protected]>
Co-authored-by: Stefano Ottolenghi <[email protected]>
Co-authored-by: Jens Pryce-Åklundh <[email protected]>
Co-authored-by: Gem Lamont <[email protected]>