Add support for 'require' option to facilitate loading of modules via `require('module')`

Exposes a module to be accessed from outside the module file using `require(file)`. Uses the filename as the exposed module name.

See [node-browserfy](https://github.com/substack/node-browserify#brequirefile-opts) documentation for more info.

```javascript
gulp.task('browserify', function () {
  gulp.src(['./test.js'])
    .pipe(browserify({
        require: ['expose']
      })) 
      .pipe(gulp.dest('./modules/'));
});
```

The above code will convert `/test.js` into `/modules/test.js`. Once included on a page via a script tag, can be loaded by `require('./modules/test.js')`