Release 0.6.0

Test with

```shell
cd /tmp
rm -rf node_modules
npm install onsip/SIP.js#prerelease-0.6.0
cd node_modules/sip.js
npm install
grunt
```

You can also use `bower`:

```shell
cd /tmp
rm -rf bower_components
bower install onsip/SIP.js#prerelease-0.6.0
```

![image](https://cloud.githubusercontent.com/assets/6473925/3514910/85f6c4f2-06d0-11e4-979e-fec1e9cca3d3.png)