介绍GWT API的英文版的电子书，
Asynchronous JavaScript and XML (Ajax) development is hard. Not ascending-
Everest hard, maybe not even calculating-your-taxes hard, but hard. This is true for
a number of reasons: JavaScript can require a lot of specialized knowledge and discipline,
browsers have slightly different implementations and feature sets, tooling is
still immature, and debugging in multiple environments is problematic. All of
these factors add up to developers needing a vast knowledge of browser oddities
and tricks to build and manage large Ajax projects.
