cache some functions for faster access
cache some functions for faster access

we use these when doing heavily redundant operations, so make access path as short as possible

koreader/koreader-base,apletnev/koreader-base,NiLuJe/koreader-base,NiLuJe/koreader-base,NiLuJe/koreader-base,houqp/koreader-base,Hzj-jie/koreader-base,Frenzie/koreader-base,frankyifei/koreader-base,apletnev/koreader-base,frankyifei/koreader-base,houqp/koreader-base,Frenzie/koreader-base,Frenzie/koreader-base,frankyifei/koreader-base,Hzj-jie/koreader-base,koreader/koreader-base,houqp/koreader-base,koreader/koreader-base,koreader/koreader-base,apletnev/koreader-base,Hzj-jie/koreader-base,Frenzie/koreader-base,apletnev/koreader-base,NiLuJe/koreader-base,frankyifei/koreader-base,houqp/koreader-base,Hzj-jie/koreader-base