Website post-processing: Reindent to < 80 cols

• Try to follow PEP8 suggestions and avoid the backslash character to force line continuation. Use parentheses instead, where possible. See https://www.python.org/dev/peps/pep-0008/#maximum-line-length
• Break before binary operators See https://www.python.org/dev/peps/pep-0008/#should-a-line-break-before-or-after-a-binary-operator

Tested with make WEB_TARGETS='offline online' LANGS='' and comparing out-www against a version without this MR applied. The only diffs were in

out-www/offline-root/input/regression/lilypond-book/collated-files.pdf
out-www/online-root/input/regression/lilypond-book/collated-files.pdf
out-www/xref-maps/collated-files.xref-map

what I think is expected.