Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/split_column.md

@@ -0,0 +1,18 @@
+---
+title: split column
+layout: command
+version: 0.59.0
+---
+
+splits contents across multiple columns via the separator.
+
+## Signature
+
+```> split column (separator) ...rest --collapse-empty```
+
+## Parameters
+
+ -  `separator`: the character that denotes what separates columns
+ -  `...rest`: column names to give the new columns
+ -  `--collapse-empty`: remove empty columns
+