use fractional sleep as a fallback for devices where usleep isn't present
use fractional sleep as a fallback for devices where usleep isn't present

pazos/koreader,poire-z/koreader,Hzj-jie/koreader,houqp/koreader,Frenzie/koreader,mwoz123/koreader,koreader/koreader,NiLuJe/koreader,mihailim/koreader,poire-z/koreader,Markismus/koreader,koreader/koreader,Frenzie/koreader,NiLuJe/koreader