Use readlink to read symbolic instead cd

Introduced readlink to read symbolic link in ~/.marks/ without need to cd to the link location and back. Thanks to a comment of [seidler2547](https://twitter.com/seidler2547/status/497444546926886912).
Are you using ` set -gx CDPATH . ~ $CDPATH` in `fish.conf` ?

Anyway, my email is kidpixo@gmail.com, contact me there or via chat for quick answer.