##demo是对写好的一个NSObject的methodSwizzing分类进行的测试代码。 替换主要是使用ClassB的funcB方法来替换ClassA的funcA方法，然后调用ClassA的funcA方法来查看是否替换成功。
##使用方法，包含两个NSObject+方法，例子：
实例方法的替换（-方法）
[NSObject zh_swizzleClass:[ClassA class] original:@selector(funcA) withSwizzedClass:[ClassB class] swizzledSelector:@selector(funcB)];
类方法的替换 （+方法）
[NSObject zh_swizzleMetaClass:[ClassA class] original:@selector(funcA) withSwizzedClass:[ClassB class] swizzledSelector:@selector(funcB)];
##分别测试了不同场景下的使用结果，测试场景如下：
condition1: ClassB dosen't have funcB
expect: swizze failed
result：swizze failed
condition2: ClassA has nothing, ClassB has funcB
expect: ZHClassBCondition2 funcB
result：swizze sucess
condition3: ClassA has funcA, ClassB has funcB
expect: ZHClassBCondition3 funcB + ZHClassACondition3 funcA
result：swizze sucess
condition4: ClassA has funcB, ClassB has funcB
expect: ZHClassBCondition4 funcB
result：swizze sucess
condition5: ClassA has funcA and funcB, ClassB has funcB
expect: class:ZHClassACondition5 already has method:funcB + ZHClassACondition5 funcA
result：swizze failed
condition6: ClassA has funcA:, ClassB has funcB
expect: Trying to swizze methods with different typeEncodeing + ZHClassACondition6 funcA str = aaa
result：swizze failed
testClassMethodSwizzing: classMehtod swizzing
expect: ZHClassBCondition7 funcB
result：swizze sucess
testClassMethodSwizzing: swizz class method with instance method
expect: ZHClassBCondition6 funcB
result：swizze sucess