Proofread and improve the whole class reference

- Document a few more properties and methods
- Add more information to many classes
- Fix lots of typos and gramar mistakes
- Use [code] tags for parameters consistently
- Use [b] and [i] tags consistently
- Put "Warning:" and "Note:" on their own line to be more visible,
  and make them always bold
- Tweak formatting in code examples to be more readable
- Use double quotes consistently
- Add more links to third-party technologies

doc/classes/ScriptCreateDialog.xml

@@ -7,8 +7,8 @@
 		The [ScriptCreateDialog] creates script files according to a given template for a given scripting language. The standard use is to configure its fields prior to calling one of the [method Popup.popup] methods.
 		[codeblock]
 		func _ready():
-		    dialog.config("Node", "res://new_node.gd") # for in-engine types
-		    dialog.config("\"res://base_node.gd\"", "res://derived_node.gd") # for script types
+		    dialog.config("Node", "res://new_node.gd") # For in-engine types
+		    dialog.config("\"res://base_node.gd\"", "res://derived_node.gd") # For script types
 		    dialog.popup_centered()
 		[/codeblock]
 	</description>