Gulp Version

this pr modifies the transform to be fully gulp-ready. It currently lacks support to file streams (it is supporting only the default - buffer). 

Something crazy is happening: it is doing it all right for a single file (`gulp.src('files/file.xml')`) but it throws an exception when i try to use it for more (`gulp.src(files/*.xml)`). The stacktrace is the following:

```
Error: junk after document element in line 11037
    at parseChunk (/home/ciro/Development/Javascript/cvc-converter/node_modules/xml-stream/lib/xml-stream.js:510:26)
```