doc: replace . as self-index operator with ::

doc/sample/Person.im

@@ -94,23 +94,23 @@ class Person
 
        In this case, the getter has been set to a variable. To facilitate this
        functionality, the compiler converts this to a lambda of the form
-            [ ^self.val ]
+            [ ^self::val ]
        that will be evaluated when the getter is invoked
 
        Similarly, the compiler synthesizes a lambda for the setter as well.
        Here, the expression
-            self.val = value
+            self::val = value
        is converted to the lambda
-            [ :x | self.val = x ]
+            [ :x | self::val = x ]
     */
-    $ exampleProperty | get => self.val, set => self.val = value.
+    $ exampleProperty | get => self::val, set => self::val = value.
 
     /* Without the lambda synthesis, the property would look like this:
        Note that this is the only time it is legal to access private fields
        via `self` from a lambda. */
     $ exampleProperty |
-        get => [ ^self.val ],
+        get => [ ^self::val ],
-        set => [ :x | self.val = x ].
+        set => [ :x | self::val = x ].
 
     /* The `get` element of a property doesn't have to be a lambda, it can
        be any value. When the property is accessed, the value provided will
@@ -497,12 +497,12 @@ end
 
     for situations where you want to return the recipient after a chain of
     cascaded messages, you can use the -yourself message, which is understood by
-    all objects by default and always returns the object itself.
+    all objects by default and always returns the object itself::
  **/
 
 p1 = Person new(name:'John Doe' age:34);
     setAge:100 inUnit:#months;
-    yourself.
+    yourself::
 
 /* p1 now contains the Person object */
 /* again, with do..end */