Minor refactoring, added OP_GETMETHOD

You can use ':' without invoking. So you can grab a method binding to an object and later call it. Also some GC bugs were fixed.

A new preprocessor macro (VM_DEBUG) has been added. Defining this macro will print each instruction thats being executed in the VM, as
well as print each call.

src/coperators.h

@@ -29,6 +29,7 @@ typedef enum {
     OP_NEWOBJECT,
     OP_SETOBJECT,
     OP_GETOBJECT,
+    OP_GETMETHOD,
     OP_INVOKE,
     OP_ITER,
     OP_NEXT,