Fix simple citations by making prefixes and suffixes optional.

src/parser/object_parser.rs

@@ -8,6 +8,7 @@ use super::regular_link::regular_link;
 use super::Context;
 use crate::error::Res;
 use crate::parser::angle_link::angle_link;
+use crate::parser::citation::citation;
 use crate::parser::entity::entity;
 use crate::parser::export_snippet::export_snippet;
 use crate::parser::footnote_reference::footnote_reference;
@@ -28,6 +29,10 @@ pub fn standard_set_object<'r, 's>(
     not(|i| context.check_exit_matcher(i))(input)?;
 
     alt((
+        map(
+            parser_with_context!(citation)(context),
+            Object::Citation,
+        ),
         map(
             parser_with_context!(footnote_reference)(context),
             Object::FootnoteReference,