OC：Masonry小结

对于在ViewController内，使用mas_XXXLayoutGuide
对于在View内，推荐使用mas_XXXMargin
如（self为控制器）：

    [greenView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.bottom.equalTo(self.mas_bottomLayoutGuide);
        make.left.right.equalTo(@0);
        make.height.equalTo(@100);
    }];

等价于：

    [greenView mas_makeConstraints:^(MASConstraintMaker *make) {
        make.bottom.equalTo(self.view.mas_bottomMargin);
        make.left.right.equalTo(@0);
        make.height.equalTo(@100);
    }];