Please support shorter constructor init

[Danilo Krahn]

Please add `this` and `super` to constructor parameters.

Old style:
```d
  struct Rectangle {
     int x,y,width,height;
     Color color;

     this(int x, int y, int width, int height, Color color) {
         this.x = x;
         this.y = y;
         this.width = width;
         this.height = height;
         this.color = color;
     }
}
```

New style. Shorter. Less to type:
```d
struct Rectangle {
     int x,y,width,height;
     Color color;

     this(this.x, this.y, this.width, this.height, this.color) {}
}
```

Constructor initialization is annoying and often repeating.
Make it shorter. Nicer.

`this` and `super` can be directly supported in constructor 
parameters. It would save lots of typing.

The code:
```d
module app;

class Vector2D {
     float x, y;
     this(int x, int y) {
         this.x = x;
         this.y = y;
     }
}

class Vector3D : Vector2D {
     float z;
     this(int x, int y, int z) {
         super(x,y);
         this.z = z;
     }
}

void main() {
     auto v1 = new Vector2D(10,20);
}
```
could be shortened to:
```d
module app;

class Vector2D {
     float x, y;
     this(this.x, this.y);
}

class Vector3D : Vector2D {
     float z;
     this(super.x, super.y, this.z);
}

void main() {
     auto v1 = new Vector2D(10,20);
}
```
or ```d
module app;

class Vector2D {
     float x, y;
     this(this.x, this.y) {}
}

class Vector3D : Vector2D {
     float z;
     this(super.x, super.y, this.z) {}
}

void main() {
     auto v1 = new Vector2D(10,20);
}
```