Added option to choose output file

I added the functionality of being able to choose where the output should be.
The way i've implemented this is in the first line of the less file you put:

```
//out: some/folder/file.css
```

So if the first line starts with //out: it will be read and interpreted as filepath.
If the path exists the file will be put there, otherwise the directories will be automatically created.

I think this is good solution at least till you find a better way(per project customization).

Also please forgive me for the inclusion of node_modules, i didn't know other way to include the modules and make the extension work in brackets. Also a note: Added module dependency is mkpath