Adds support for inclusion of variables defined in the gulpfile.js

var fileInclude = require('gulp-file-include');

```javascript
gulp.task('html', function() {
  return gulp.src([ '*.html' ])
             .pipe(fileInclude({
               data: {
                 "title": "Default Page Title"
               }
             })
             .pipe(gulp.dest('public'));
});
```

The variables can be overridden by individual `@@include(...)` statements

```
@@include("index.html", { "title": "The Homepage" })
```