Filters support

Support for filtering files:
```javascript
var tsResult = gulp.src('...')
    .pipe(ts(project));

tsResult.pipe(ts.filter(project, { referencedFrom: 'main.js' })) ...
```
and
```javascript
var tsResult = gulp.src('...')
    .pipe(ts(project, { referencedFrom: 'main.js' }));
...
```