Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/par-each.md

@@ -0,0 +1,24 @@
+---
+title: par-each
+layout: command
+version: 0.59.0
+---
+
+Run a block on each element of input in parallel
+
+## Signature
+
+```> par-each (block) --numbered```
+
+## Parameters
+
+ -  `block`: the block to run
+ -  `--numbered`: iterate with an index
+
+## Examples
+
+Multiplies elements in list
+```shell
+> [1 2 3] | par-each { 2 * $it }
+```
+