 cre.cpp: adds getPrevVisibleWordStart(), getNextVisibleWordEnd() (#808)
 cre.cpp: adds getPrevVisibleWordStart(), getNextVisibleWordEnd() (#808)

and friends. Will allow moving highlights edges.
NiLuJe/koreader-base,Frenzie/koreader-base,koreader/koreader-base,houqp/koreader-base,NiLuJe/koreader-base,houqp/koreader-base,koreader/koreader-base,houqp/koreader-base,NiLuJe/koreader-base,koreader/koreader-base,houqp/koreader-base,Frenzie/koreader-base,Frenzie/koreader-base,koreader/koreader-base,Frenzie/koreader-base,NiLuJe/koreader-base