v0.17.1 — distinct labels for narrow-range breaks

Fixed

• Continuous axis and legend breaks are labelled jointly
  (scale::util::format_numbers): on narrow ranges neighbouring breaks get
  enough decimals to stay distinct (0.99, 0.992, 0.994 instead of
  0.99, 0.99, 0.99), and a non-zero break never prints as 0 (log ticks at
  0.001). Labels are unchanged wherever two decimals already suffice;
  custom label_* formatters are unaffected.