Local path option, command tokens, and delayed symlink change.

* Added a config option to specify where the deploy should be sourced from, but it still defaults to the current path.
* Added command tokens that will be replaced by the appropriate value:
** $LOCAL_PATH resolves to options.local_path
** $DEPLOY_PATH resolves to options.release_path
** $RELEASE_PATH resolves to the complete release path that is generated by the script (eg, /path/to/deploy/path/releases/20131116000000/)
* Delayed the moving of the symlink until after the deploy is finished to prevent any outages. It may make sense to deploy this even further until after the post commands have been run.