Base: Move GML documentation into subsection

That was the whole point of this endeavour :^)

Base/usr/share/man/man5/GML/Widget-CheckBox.md

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+## Name
+
+GML Checkbox Widget
+
+## Description
+
+Defines a GUI checkbox widget.
+
+## Synopsis
+
+`@GUI::CheckBox`
+
+## Examples
+
+```gml
+@GUI::CheckBox {
+    name: "top_checkbox"
+    text: "Checkbox"
+}
+
+@GUI::CheckBox {
+    name: "bottom_checkbox"
+    text: "Disabled"
+    enabled: false
+}
+```
+
+## Registered Properties
+
+| Property          | Type   | Possible values   | Description                                                        |
+|-------------------|--------|-------------------|--------------------------------------------------------------------|
+| autosize          | bool   | true or false     | Determines if auto-sized                                           |
+| checkbox_position | String | "Left" or "Right" | Place the checkbox itself on either the left or right of its label |
+
+## See also
+- [GML Button](help://man/5/GML/Widget-Button)