Treeview Docs

Added Treeview docs
Improved some stuff in the treeview object

docs/objects/Treeview/setExpanded.md

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+## setExpanded
+
+### Description
+
+The `setExpanded` method sets the expanded state of a specified node within a Treeview object. When a node is expanded, its children nodes are displayed. If a node is collapsed, its children nodes are hidden.
+
+### Parameters
+
+1. `boolean` The expanded state to set for the node (true for expanded, false for collapsed)
+
+### Returns
+
+1. `object` The object in use
+
+### Usage
+
+* Creates a Treeview, adds a child node to the root node, and sets the expanded state to false:
+
+```lua
+local basalt = require("basalt")
+
+local mainFrame = basalt.createFrame()
+local treeview = mainFrame:addTreeview()
+
+local rootNode = treeview:getRoot()
+local childNode = rootNode.addChild("Child Node")
+
+rootNode.setExpanded(false)
+
+basalt.autoUpdate()
+```
+
+In this example, a Treeview object is created and added to the mainFrame. The `getRoot` method is used to access the root node, and a new child node is added to it using the `addChild` method. The `setExpanded` method is then used to set the expanded state of the root node to false, hiding its children nodes.