Add memory and register checking when required in the VM

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/vm/obj/assemble/mod.rs

@@ -54,7 +54,6 @@ impl<'a> Assemble<'a> {
                     });
                 }
             }
-
             self.symbols.globals_mut().extend(exports);
         }
 
@@ -151,6 +150,8 @@ impl<'a> Assemble<'a> {
                         }
                     }
                 }
+                // TODO : make sure we aren't trying to export anything that doesn't exist
+
                 // only return exports if specified
                 if export {
                     labels.retain(|k, _| exports.contains(k));