Sort implementations alphabetically

For consistency and easier testing, we sort the implementation items
alphabetically by their name and their definitions.

CHANGELOG.md

@@ -15,6 +15,7 @@ SPDX-License-Identifier: MIT
   - Show the definition for constants and typedefs.
   - Fix group and ID for typdef items.
   - Extract the description of module items as HTML instead of plain text.
+  - Sort implementations alphabetically.
 
 ## v0.1.2 (2020-07-25)
 

src/parser.rs

@@ -484,6 +484,8 @@ fn get_implementation_group(
         }
     }
 
+    impls.sort();
+
     Ok(impls.into_member_group(Some(title.to_owned())))
 }
 
@@ -578,6 +580,14 @@ impl<'a> MemberDocs<'a> {
         }
     }
 
+    pub fn sort(&mut self) {
+        self.docs.sort_by(|d1, d2| {
+            d1.name
+                .cmp(&d2.name)
+                .then_with(|| d1.definition.cmp(&d2.definition))
+        })
+    }
+
     pub fn push(
         &mut self,
         name: &mut Option<String>,