Added wp_config_permissions to allow changing wp-config.php permissions and ${wp_lang} as part of the name of the downloaded tar.gz 

In some environments, creating wp-config.php with 0755 permissions can be unsecure, because it contains sensitive data, like the database password, in plain text.

This change, allows the user to specify another value (like 0600, more convenient in shared servers) but leaves default value unchanged (0755) so working projects should not be affected.

This pull request also re-adds #40 changes that were overwritten by #36.