Adds a sparkline(array|map) built-in that renders numeric values as a
Unicode block-character string (▁▂▃▄▅▆▇█), plus a new `mlr sparkline`
verb that summarizes each field's values in record order -- useful for
eyeballing trends without external plotting tools.
Also adds `-s` to `mlr histogram` to sparkline a field's binned counts
(its distribution shape) rather than emitting one record per bin. This
is a different chart from `mlr sparkline` (order-independent binning
vs. record-order values), and the docs for each cross-reference the
other to avoid conflating them.
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
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