Auto-Generate Documentation for nushell.com (#2139)

* Very rough idea

* Remove colour codes

* Work on command for generating docs

* Quick comment

* Use nested collapsible markdown

* Refine documentation command

* Clippy and rename docs

* This layout probably seems best

Also moved some code to documentation.rs to avoid making help.rs massive

* Delete summaries.md

* Add usage strings

* Remove static annotations

* get_documentation produces value

Which will be used like
'help generate_docs | save "something"'
The resulting yaml can be passed to a script for generating HTML/MD files in the website

* Fix subcommands

* DRY code

* Address clippy:

* Fix links

* Clippy lints

* Move documentation to more central location

docs/commands/split-row.md

@@ -0,0 +1,34 @@
+# split row
+
+splits contents over multiple rows via the separator.
+
+Syntax: `split row <separator>`
+
+## Parameters
+
+* `<separator>` the character that denotes what separates rows
+
+## Examples
+
+We can build a table from a file that looks like this
+
+```shell
+> open table.txt
+4, 0, 2, 0, 7, 8
+```
+
+using the `split row` command.
+
+```shell
+open table.txt | split row ", "
+───┬───
+ # │
+───┼───
+ 0 │ 4
+ 1 │ 0
+ 2 │ 2
+ 3 │ 0
+ 4 │ 7
+ 5 │ 8
+───┴───
+```