Imutability as default

[sergiotaborda]

• make all types immutable as default
• change the keywork immutable to mutable
  • validade imutability rules
• value classes remain immutable
• muatbility must be marked in classes instead of immutability
• remove let/val from. primary constructors and properties. allow for mutable keyword

public mutable name : String? instead of public name string? {get; set; } and public name: String?

• if a property is mutable the type must be mutable
• methods may not mutate state only constructors may set state

public mutable class Person { // forced mutable, because one property is mutable

  public constructor (
       public mutable name: String;  // mutable. meaning it as a set and a get
       public birthday : Date;  // immutable. it only has a get
  );
}