Create CSS stylesheets from rules

Add an additional module that allows for a CSS file to be generated based off rules.

```sass
.error {
level: error;
// to
border: 1px solid red;
}

.warning {
level: warning;
// to
border: 1px solid orange;
}

.info {
level: info;
// to
border: 1px solid blue;
}
```