Added Avatar() into Author

This commit adds the Avatar method into the Author interface. It returns
the URL if one, or it can return an empty string if either the service
does not support avatars or the user doesn't have avatars.

cchat.go

@@ -211,6 +211,9 @@ type Authenticator interface {
 type Author interface {
 	Identifier
 
+	// Avatar returns the URL to the user's avatar or an empty string if they have
+	// no avatar or the service does not have any avatars.
+	Avatar() (url string)
 	Name() text.Rich
 }
 

repository/main.go

@@ -597,6 +597,17 @@ var Main = Packages{
 						Type: MakeQual("text", "Rich"),
 					}},
 				},
+				GetterMethod{
+					method: method{
+						Comment: Comment{`
+							Avatar returns the URL to the user's avatar or an
+							empty string if they have no avatar or the service
+							does not have any avatars.
+						`},
+						Name: "Avatar",
+					},
+					Returns: []NamedType{{Name: "url", Type: "string"}},
+				},
 			},
 		}, {
 			Comment: Comment{`