Add scd plugin for smart change of directory.

Synced with the scd-tracker branch pavoljuhas/oh-my-zsh@9d04d8ca78030d4c9af4bf0f58b49532a6ef1b35
Merge branch 'master' of https://github.com/robbyrussell/oh-my-zsh
Add scd plugin for smart change of directory.

Synced with the scd-tracker branch
pavoljuhas/oh-my-zsh@2f78243cad3509058d142aa4b70a604e75ec741e.
Merge pull request #2510 from pavoljuhas/master

Add scd plugin for smart change of directory.