Broken SIN stuff

Thought the identity generation stuff would be easy to add to libcoin, but I am a bit stumped by the following, possibly inheritance related??

```
/home/jgarzik/node_modules/libcoin/util/EncodedData.js:37
    return this.converters[encoding].call(this);
                          ^
TypeError: Cannot read property 'base58' of undefined
    at SIN.ClassSpec.EncodedData.as (/home/jgarzik/node_modules/libcoin/util/EncodedData.js:37:27)
    at SIN.ClassSpec.EncodedData.toString (/home/jgarzik/node_modules/libcoin/util/EncodedData.js:52:17)
    at SINKey.ClassSpec.SINKey.storeObj (/home/jgarzik/node_modules/libcoin/SINKey.js:30:13)
    at Object.<anonymous> (/home/jgarzik/node_modules/libcoin/sin-test.js:6:16)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
```