You can now register a click event handler on a button.
You can now add a text box to a window.
A text box now properly reports its text value when you change it in the gui instead of in code.
Added common properties for values.
Renamed common.text to common.label to closer represent the way it works.
Metatables don't store a list of class instances anymore, since every instance has its own metatable now.
Moved the code to verify the type of a parameter to a separate function.