CrossLink inner content

I was interested by using the inner contents of CrossLink tag, so i've just code it. (as  already request in issue #64)

when `crossLink` et `crossLinkModule`  contains some content, it's used instead of the default value.

```
{{#crossLink "myClass" }}An awesome class{{/crossLink}}
{{#crossLinkModule "Module" }}The main module{{/crossLinkModule}}
```

Please, have a look to this code.