Add a make target for running `codespell` on all sources.
Skip running codespell on the build directory (we have javascript etc.
in there).
Only emit warnings but do not fail on spelling errors in diagrams.
Signed-off-by: David Runge <dave@sleepmap.de>
To be on the safe side, always build HTML pages from scratch, so that
lychee checks the actual current version of the files.
Signed-off-by: David Runge <dave@sleepmap.de>
