Returns the ID of an iPaper, given its url. Can also be used to check whether a url is vacant.
Sample Response When iPaper Not Found
<?xml version="1.0" encoding="utf-8"?>
<result>
<code><![CDATA[SUCCESS]]></code>
<message><![CDATA[Paper not found.]]></message>
</result>
Sample Response When iPaper Is Found
<?xml version="1.0" encoding="utf-8"?>
<result>
<code><![CDATA[SUCCESS]]></code>
<message><![CDATA[Paper found.]]></message>
<data>
<paper id="1106" />
</data>
</result>