chore: rename StartReturningModel to Run

Added aliases for the old functions, but deprecated them.

tutorials/basics/README.md

@@ -200,7 +200,7 @@ The last step is to simply run our program. We pass our initial model to
 ```go
 func main() {
     p := tea.NewProgram(initialModel())
-    if err := p.Start(); err != nil {
+    if _, err := p.Run(); err != nil {
         fmt.Printf("Alas, there's been an error: %v", err)
         os.Exit(1)
     }