docs: talk about write-masking for polarcoord example

also finish the text on polarcoord

Signed-off-by: Matthias Kretz <kretz@kde.org>
add simple script to rebuild api docs automatically

run this script in the background while you work on the docs to get them
updated automatically whenever you save your changes

Signed-off-by: Matthias Kretz <kretz@kde.org>
finitediff example: use constexpr

Signed-off-by: Matthias Kretz <kretz@kde.org>
finitediff docs: boilerplate work (snippets)

Signed-off-by: Matthias Kretz <kretz@kde.org>