Add html ids to headlines

Sources/Generator/Extensions/String+Extensions.swift

@@ -82,6 +82,10 @@ extension Substring {
     func between(first: String, andLast last: String) -> String {
         dropBeforeFirst(first).dropAfterLast(last)
     }
+
+    func last(after: String) -> String {
+        components(separatedBy: after).last!
+    }
 }
 
 extension String {