add more easymotion commands

[lnfuhl]

Mapping s/f/t directly to sn/fn/tn in a flash-like motion like idea-easymotion. This means that the s/f/t can be used on the basis of the original, and the many characters can be directly entered to search. It can refer to https://github.com/AlexPl292/IdeaVim-EasyMotion.