loader imports
type en/decode just wrap their codec.
first transformer works!

```
node
> var transformer = require('./index');
> var json2xml = transformer('json-codec', 'xml-codec');
> var input = JSON.stringify({foo:'bar'});
> json2xml(input)
'<?xml version="1.0" encoding="UTF-8" standalone="yes"?>\n<foo>bar</foo>'
```