Make changes to have wechat-rails running in Ruby 1.9

1. Get rid of keyword arguments;
2. Use Array.include? to test if an element is in an array.

Some trailing white spaces are also cleaned up in this commit.
Hm I think we should keep code/style changes as minimal as possible if we hope to merge the changes upstream to wechat-rails. We should aim to do that, right?

This gem looks to have so many violations of our style guide that if we want to improve the style, we should fix all of them. Until then, it's probably prudent to keep style consistent with the existing code.