Treeview Docs

Added Treeview docs
Improved some stuff in the treeview object

docs/objects/Treeview/setExpandable.md

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+## setExpandable
+
+### Description
+
+The `setExpandable` method allows you to control whether a node within a Treeview object can be expanded or collapsed by the user. When a node is set to be expandable, it will show a visual indicator (such as a "+" symbol) when it has child nodes, allowing the user to expand or collapse the node by clicking on the indicator.
+
+### Parameters
+
+1. `boolean` A boolean value indicating whether the node should be expandable (true) or not (false).
+
+### Returns
+
+1. `node` The node in use
+
+### Usage
+
+* Creates a Treeview, adds a child node to the root node, and sets the child node to be expandable:
+
+```lua
+local basalt = require("basalt")
+
+local mainFrame = basalt.createFrame()
+local treeview = mainFrame:addTreeview()
+
+local rootNode = treeview:getRoot()
+local childNode = rootNode.addChild("Expandable Child Node")
+
+childNode.setExpandable(true)
+
+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 `setExpandable` method is then called on the child node with a true parameter, making the node expandable by the user.