Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/dfr_aggregate.md

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+---
+title: dfr aggregate
+layout: command
+version: 0.59.0
+---
+
+Performs an aggregation operation on a dataframe and groupby object
+
+## Signature
+
+```> dfr aggregate (operation-name) --quantile --explicit```
+
+## Parameters
+
+ -  `operation-name`: 
+	Dataframes: mean, sum, min, max, quantile, median, var, std
+	GroupBy: mean, sum, min, max, first, last, nunique, quantile, median, var, std, count
+ -  `--quantile {number}`: quantile value for quantile operation
+ -  `--explicit`: returns explicit names for groupby aggregations
+
+## Examples
+
+Aggregate sum by grouping by column a and summing on col b
+```shell
+> [[a b]; [one 1] [one 2]] | dfr to-df | dfr group-by a | dfr aggregate sum
+```
+
+Aggregate sum in dataframe columns
+```shell
+> [[a b]; [4 1] [5 2]] | dfr to-df | dfr aggregate sum
+```
+
+Aggregate sum in series
+```shell
+> [4 1 5 6] | dfr to-df | dfr aggregate sum
+```
+