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).
I'm not using it, it seems weird that I have to manually configure this though.
I'd rather deal with it inside the plugin.

I'll add you on gmail chat, but I'll probably not be available later.