Added feature - to set default value for var

Added feature - to set default value for var
This is a feature add, which allows you to declare default value to a class variable.

For example
Screen=(
    var color="black"
    var bgcolor="white"
    var width=300
    var height=200
    var title
    function show
    function hide
    function resize
)

Now when we create a new object
new Screen S1

By default the Class variable:
    color is set to "black"
    bgcolor is set to "white"
    width is set to "300"
    height is set to "200"

But Class variable: title is not initialized to any value

If you want you can write your Screen::__init__() function
to override default values if parameters are passed during creation of new object.