Add missing escape

Hi @noprompt,

We're looking to expand usage of frak in vim-clojure-static and I found these two little bugs in the process.

BTW, would it be possible to either have access to escape-chars or provide a custom escape function? I'd like to be able to escape vim-specific special characters like `<`, `>`, `@`, and more. There are lots of ways to implement this (dynamic var, explicit parameter, callback, etc), so I didn't prepare a patch.

Thanks!