Add self return type to methods

[dzikoysk]

class Builder {

    hidden Foo o

    method self includeFoo(Foo foo) {
        this.foo = foo
    }

}

main {
    Builder builder = new Builder()
            .includeFoo(new Foo())
}

[dzikoysk]

type Builder {
    internal Foo o

    shared includeFoo (Foo foo) -> self {
        this.foo = foo
    }
}

main {
    Builder builder = new Builder()
            .includeFoo(new Foo())
}