Add tree object
Update changelog
Add button:GetDown
Call object:GetDown in button drawing function
Update changelog
Fix #129
Check type of icon argument in treenode:SetIcon
Add treenode:GetIcon
Add treenode:SetText and treenode:GetText
Add treenode.OnOpen and treenode.OnClose event callbacks
Add missing treenode method comments
Add treenode:GetOpen
Update changelog
Fix typo in changelog