Formatting of newlines at EOF

Given the following xml:

````
<root>
    <child>value</child>
</root>


````

There are 2 issues when formatting:
* first, and most importantly: there's no way to keep a newline at EOF
* second, formatting is not idempotent: the first time it removes only 1 of the 2 trailing newlines, the second time it removes the remaining trailing newline
