Links preprocessor: support pluses in file paths

src/preprocess/links.rs

@@ -370,7 +370,7 @@ fn find_links(contents: &str) -> LinkIter<'_> {
             \{\{\s*                      # link opening parens and whitespace
             \#([a-zA-Z0-9_]+)            # link type
             \s+                          # separating whitespace
-            ([a-zA-Z0-9\s_.\-:/\\]+)   # link target path and space separated properties
+            ([a-zA-Z0-9\s_.\-:/\\\+]+)   # link target path and space separated properties
             \s*\}\}                      # whitespace and link closing parens"
         )
         .unwrap();