refactor: simplify user string conversion

src/Converters/StringConverters.cs

@@ -81,8 +81,5 @@ namespace SourceGit.Converters
 
         public static readonly FuncValueConverter<string, bool> ContainsSpaces =
             new FuncValueConverter<string, bool>(v => v != null && v.Contains(' '));
-        
-        public static readonly FuncValueConverter<Models.User, string> UserToString =
-            new FuncValueConverter<Models.User, string>(v => v == null ? string.Empty : $"{v.Name} <{v.Email}>");
     }
 }

src/Models/User.cs

@@ -43,6 +43,11 @@ namespace SourceGit.Models
             return _caches.GetOrAdd(data, key => new User(key));
         }
 
+        public override string ToString()
+        {
+            return $"{Name} <{Email}>";
+        }
+
         private static ConcurrentDictionary<string, User> _caches = new ConcurrentDictionary<string, User>();
         private readonly int _hash;
     }

src/Views/Histories.axaml

@@ -166,7 +166,7 @@
                   <Grid Grid.Column="1"
                         ColumnDefinitions="20,*"
                         Background="Transparent"
-                        ToolTip.Tip="{Binding Author, Converter={x:Static c:StringConverters.UserToString}}">
+                        ToolTip.Tip="{Binding Author}">
                     <v:Avatar Grid.Column="0"
                               Width="16" Height="16"
                               Margin="4,0,0,0"