Allow rebasing of dependency paths

This addition will be useful when working with web server setups to overwrite relative paths. For example, if we had a directory structure like so:

```
project
  - html
  --- index.html
  - bower_components
  --- jquery
  ------ jquery.js
```

And wanted index.html to read:

```
/bower_components/jquery/jquery.js
```

instead of:

```
../bower_components/jquery/jquery.js
```

This can be done using the _-r_ option.