平分布局

利用masonry实现如下图的布局格式：

实现代码如下：

//设置约束
- (void)setTheConstraintForProgress {
    //开始
    [self.startBtn mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.equalTo(self.view.mas_top).offset(150);
        make.left.equalTo(self.view.mas_left).offset(kMargin);
        make.height.mas_equalTo(39);
    }];
    //暂停
    [self.pauseBtn mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.width.height.equalTo(self.startBtn);
        make.left.equalTo(self.startBtn.mas_right).offset(kMargin);
        make.right.equalTo(self.continueBtn.mas_left).offset(-kMargin);
    }];
    //继续
    [self.continueBtn mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.width.height.equalTo(self.startBtn);
        make.left.equalTo(self.pauseBtn.mas_right).offset(kMargin);
        make.right.equalTo(self.againBtn.mas_left).offset(-kMargin);
    }];
    //重新
    [self.againBtn mas_makeConstraints:^(MASConstraintMaker *make) {
        make.top.width.height.equalTo(self.startBtn);
        make.right.equalTo(self.view.mas_right).offset(-kMargin);
    }];
}