Fix #6 Now you can also return value from define function like can be done with require.js

For example

    define(function(require, exports, module){

        var logic = {
            a: 3
        }
        return logic;
    });

will now work.

But this will continue to work too

    define(function(require, exports, module){

        var logic = {
            a: 3
        }
        exports.a= logic.a;
    });
And tests for these modules:

``` js
define(function(require, exports, module) {
  function Test() {}
  module.exports = new Test();
});

define(function(require, exports, module) {
  module.exports = undefined;
});
```