include the standard deviation of "inbreeding" measurements

this adds $.diversity.e to the output of inbreeding load and input of inbreeding plot to show errors bars in the final plot.

these can be discarded by running something similar to

inbreeding load $experiment
    | reject diversity.e
    | inbreeding plot --options { k: $OPTS.k }

bins/inbreeding/load.nu

@@ -46,8 +46,10 @@ export def main [
                 | parse "{x}, {y}"
                 | into float y
                 | group-by x --to-table
-                | update items { get y | math avg }
-                | rename --column { group: "x", items: "y" }
+                | insert y { get items.y | math avg }
+                | insert e { get items.y | math stddev }
+                | rename --column { group: "x" }
+                | reject items
                 | into int x # NOTE: $.x needs to be converted to int here because
                              # `group-by --to-table` converts the grouping key to
                              # string