Implement reference counting (#592)

tests/compiler/rc/local-init.ts

@@ -0,0 +1,26 @@
+{
+  // Normal assignment will retain and release.
+
+  let a = /* __retain( */ "" /* ) */;
+  // __release(a)
+}
+
+function getRef(): string {
+  return /* __retain( */ "" /* ) */;
+}
+
+{
+  // Assignment of a return value picks up its skipped autorelease
+
+  let b = getRef();
+  // __release(b);
+}
+
+class Ref {}
+
+{
+  // Assignment of an instantiation picks up its skipped autorelease
+
+  let c = new Ref();
+  // __release(c);
+}