`buildXmlInput` and `deepToArray` don't allow single-wrapper arrays

[benbuckman]

The module is trying to be smart in converting the input JSON params to XML. See deep-to-array.test.js and xml-request.test.js.

So given an input param thing: ['a', 'b', 'c'], it converts that to

<thing>a</thing>
<thing>b</thing>
<thing>c</thing>

But if we want to do something like,

<OrderIDArray>
  <OrderID>aaaa</OrderID>
  <OrderID>bbbb</OrderID>
</OrderIDArray>

This doesn't seem currently possible.

Should the module try to stay smart, and somehow differentiate these? Or should the input param structure simply follow the xml module's pattern without conversion?