Convert <newline> inside <item> and <newline effect="normal"> inside <para>

<newline effect="underline"/> inside a <para> results in invalid HTML.
I don't know if we should convert it anyway or not.  Right now we'll get
"NOT_CONVERTED_YET".

I tried it on the index.cnxml of the example that Ed gave http://desert.cnx.rice.edu/contents/fe05a681-fab0-48f0-be12-db6a8eb05aaa:6 and it now transforms all the `<newline/>`s.