HtmlFormat.escape loop performance

The following loop could probably be a bit faster if a `while` loop is used instead of a `foreach` expression. Might save some character boxing and the code would still be pretty simple.

```scala
  def escape(text: String): Html = {
    // Using our own algorithm here because commons lang escaping wasn't designed for protecting against XSS, and there
    // don't seem to be any other good generic escaping tools out there.
    val sb = new StringBuilder(text.length)
    text.foreach {
      case '<' => sb.append("&lt;")
      case '>' => sb.append("&gt;")
      case '"' => sb.append("&quot;")
      case '\'' => sb.append("&#x27;")
      case '&' => sb.append("&amp;")
      case c => sb += c
    }
    new Html(sb.toString)
  }
```

Cc @pvlugter.