appropriating Shailen's excellent Futures intro into tutorial

src/site/articles/using-future-based-apis/code/example3.dart

-import 'dart:io';
-import 'dart:async';
-
-void printDailyNewsDigest() {
-  File file = new File("dailyNewsDigest.txt");
-  Future future = file.readAsString();
-  future.then((content) => doSomethingWith(content))
-        .catchError((e) => handleError(e));
-}
-
-void main() {
-  printDailyNewsDigest();
-  printWinningLotteryNumbers();
-  printWeatherForecast();
-  printBaseballScore();
-}
-
-doSomethingWith(content) {
-  print('do something with content');
-}
-
-handleError(e) {
-  print('handleError');
-}
-
-printWinningLotteryNumbers() {
-  print('Winning lotto numbers: [23, 63, 87, 26, 2]');
-}
-
-printWeatherForecast() {
-  print('Tomorrow\'s forecast: 70F, sunny.');
-}
-
-printBaseballScore() {
-  print('Baseball score: Red Sox 10, Yankees 0');
-}