大中小三種字型與自适應高度字型

#define BGFont(x) [UIFont systemFontOfSize:x]
#define BGBoldFont(x) [UIFont boldSystemFontOfSize:x]
#define BGMediumFont(x) ([UIFont fontWithName:@"PingFangSC-Medium" size:x])      

#ifndef kScreenWidth
#define kScreenWidth YYScreenSize().width
#endif
#define BaseSize(x)   (kScreenWidth*(x)/375.0)
#define SystemFontOfSize(x) [UIFont systemFontOfSize:BaseSize(x)]
#define SystemMediumFontOfSize(x) ([UIFont fontWithName:@"PingFangSC-Medium" size:BaseSize(x)])