Added feature - readonly class variable

This is a feature add, which allows you to declare a readonly class variable

Syntax:

Human=(
    var name
    var age

    # Read only variable with default value
    readonly:var eyes=2

    # Read only variable ( no default value - value to be set at __init__ )
    readonly:var gender
    function eat
    function sleep
}


In the above example Humans created with readonly variable 'gender'
In this case variable gender must be set in __init__ without fail.

Once the value is set to a readonly:var it can be read like a normal var