Key bindings; fix exit help page.
Key bindings; fix exit help page.

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