chore: rename StartReturningModel to Run

Added aliases for the old functions, but deprecated them.

examples/views/main.go

@@ -41,7 +41,7 @@ var (
 func main() {
 	initialModel := model{0, false, 10, 0, 0, false, false}
 	p := tea.NewProgram(initialModel)
-	if err := p.Start(); err != nil {
+	if _, err := p.Run(); err != nil {
 		fmt.Println("could not start program:", err)
 	}
 }