Add ability to load multiple elements in one function call in HtmlBuilder

These changes allow for much more concise templating and reduce verbosity
when a developer has a lot of scripts, images, or styles to load.

For example...

```php
{{HTML::script('js/jquery.min.js')}}
{{HTML::script('js/jquery.scrollTo-1.4.2-min.js')}}
{{HTML::script('js/jquery.localscroll-1.2.7-min.js')}}
{{HTML::script('js/foo.js')}}
{{HTML::script('js/bar.js')}}
```

...becomes...

```php
{{HTML::script(['js/jquery.min.js', 'js/jquery.scrollTo-1.4.2-min.js', 'js/jquery.localscroll-1.2.7-min.js', 'js/foo.js', 'js/bar.js'])}}
```
Signed-off-by: Walker Crouse <wcrouse@uvm.edu>