Minifier Support

Adds support for minification via [html-minifier](https://github.com/kangax/html-minifier). 

```js
var collection = HTMLing.dir('templates', null, null, true);
collection.render('index', {}); // output is minified
```

also accepts options to pass to the minifier: 

```js
var collection = HTMLing.dir('templates', null, null, {
      collapseWhitespace: true,
      collapseBooleanAttributes: true
    });
collection.render('index', {}); // output is minified
```

The arguments for these commands should probably be replaced with an options object, but I'll save that for another PR.