v4.2.0

Added

• --graph picks the finest of the six fixed graphs whose window, starting
  at the first entry, reaches the latest entry (#6). Lines stamped with the
  1900 placeholder year do not stretch the span.
• --span N{s,m,h,d,mo,y} graphs exactly N units from the first entry,
  e.g. --span 90m. It implies --graph, needs at least 6 units, and must
  fit the terminal width (--wide doubles each column); otherwise exit 2.

Changed

• The six graph classes share one constructor in GraphHash; each now only
  names its unit and window. Entries are counted with a dict lookup instead
  of a scan of the window per line.

Fixed

• A leftover debug print wrote a stray number above the graph whenever the
  window had empty buckets (20 fixtures).
• --mograph and --ygraph stepped by 365/12 and 365 days, so two buckets
  could land in the same month or year: "12 months" drew 11 columns, "10
  years" drew 9, and End Time drifted (2010-07-02 14:00:00). They now
  step on the calendar, draw every bucket, and end on the first of the
  month or year.
• The middle axis label never printed on odd-width graphs, including
  --dgraph, because its position was compared as a float.

Every *graph.output fixture that changed was regenerated and its diff
reviewed: only the stray number, the column counts, the axis labels and
End Time moved.