MRTimer 介绍
MRTimer 是一个简单的 iOS 工具，用来计算方法的执行时间。
示例代码：
- (void)viewDidLoad
{
[super viewDidLoad];
[MRTimer observeSelector:@selector(doSomething) timeIntervalBlock:^(NSTimeInterval interval) {
NSLog(@"Time interval for selector: (%@, %f), NSStringFromSelector(doSomething), interval);
}];
}
- (void)doSomething
{
[MRTimer observeBegin:MR_SELECTOR];
...
[MRTimer observeEnd:MR_SELECTOR];
}