Idea: Option for indenting <% if ... %> <% end %> erb tags.

It would be nice to have the option to keep indents in for <%if ... %> tags
e.g. 
Desired output:

```
<% if my_list.empty? %>
    <div>
        <span> Text </span>
    </div>
<% end %>
```

Current output the moment:

```
<% if my_list.empty? %>
<div>
   <span> Text </span>
</div>
<% end %>
```