Support for inline XML DTD

[kddnewton]

I got this report on prettier/plugin-xml.

<!-- demo.xml -->
 <!DOCTYPE example [
  <!ELEMENT example (item)*>
  <!ELEMENT item (name, price)>
  <!ELEMENT name (#PCDATA)>
  <!ELEMENT price (#PCDATA)>
]>
<example>
  <item>
    <name>Item 1</name>
    <price>$10.00</price>
  </item>
  <item>
    <name>Item 2</name>
    <price>$20.00</price>
  </item>
</example>

Honestly I would be totally fine with a temporary measure that just didn't crash on these kinds of inputs and skipped to the next balanced >. Then I could just copy the source text and not worry about formatting it.