For plain list items with a single child that is a paragraph, do not wrap in paragraph html tags.

This is mimicking the behavior from org-mode's HTML exporter.

src/intermediate/element.rs

@@ -1,6 +1,7 @@
 use super::comment::IComment;
 use super::keyword::IKeyword;
 use super::macros::iselector;
+use super::IPlainListSimpleItem;
 
 use super::IBabelCall;
 use super::ICenterBlock;
@@ -32,6 +33,7 @@ use futures::future::{BoxFuture, FutureExt};
 pub(crate) enum IElement {
     Paragraph(IParagraph),
     PlainList(IPlainList),
+    PlainListSimpleItem(IPlainListSimpleItem),
     CenterBlock(ICenterBlock),
     QuoteBlock(IQuoteBlock),
     SpecialBlock(ISpecialBlock),