Use more conventional syntax for constructors.

They are now invoked like "new Foo".
Also, superclass constructors are now much less semantically
and syntactically weird. Since the instance is created before
any constructor is called, there's no point in time where the
instance isn't there.

benchmark/method_call.wren

@@ -1,5 +1,5 @@
 class Toggle {
-  this new(startState) {
+  new(startState) {
     _state = startState
   }
 
@@ -11,7 +11,8 @@ class Toggle {
 }
 
 class NthToggle is Toggle {
-  this new(startState, maxCounter) super.new(startState) {
+  new(startState, maxCounter) {
+    super(startState)
     _countMax = maxCounter
     _count = 0
   }
@@ -31,7 +32,7 @@ var start = OS.clock
 var n = 1000000
 var i = 0
 var val = true
-var toggle = Toggle.new(val)
+var toggle = new Toggle(val)
 
 while (i < n) {
   val = toggle.activate.value
@@ -41,7 +42,7 @@ while (i < n) {
 io.write(toggle.value)
 
 val = true
-var ntoggle = NthToggle.new(val, 3)
+var ntoggle = new NthToggle(val, 3)
 
 i = 0
 while (i < n) {