Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/drop_column.md

@@ -0,0 +1,16 @@
+---
+title: drop column
+layout: command
+version: 0.59.0
+---
+
+Remove the last number of columns. If you want to remove columns by name, try 'reject'.
+
+## Signature
+
+```> drop column (columns)```
+
+## Parameters
+
+ -  `columns`: starting from the end, the number of columns to remove
+