Added "subtemplating" for lack of a better work

[malomalo]

The following changes allow the following:

Giving this function

formTag = function (template) {
  return '<form>\n'+template()+'\n</form>';
}

The following ejs template:

<%= formTag(function () { %>
    <input type="submit" />
<% }) %>

generates:

<form>
    <input type="submit" />
</form>