Simplify hint-string generation; fix tests.
Simplify hint-string generation; fix tests.

decaffeinate-examples/vimium,smblott-github/vimium,mrmr1993/vimium,gdh1995/vimium,philc/vimium,poacher2k/vimium,decaffeinate-examples/vimium,gdh1995/vimium,philc/vimium,philc/vimium,poacher2k/vimium,mrmr1993/vimium,gdh1995/vimium,willsALMANJ/vimium,smblott-github/vimium,smblott-github/vimium,mrmr1993/vimium,poacher2k/vimium,willsALMANJ/vimium,willsALMANJ/vimium,decaffeinate-examples/vimium