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/cvm.h

@@ -6,6 +6,8 @@
 #include "cosmo.h"
 #include "cstate.h"
 
+//#define VM_DEBUG
+
 typedef enum {
     COSMOVM_OK,
     COSMOVM_RUNTIME_ERR,