Amazon S3 Expiring Link Options

Default settings for [mbr_s3_link] shortcode.

1. Your Amazon S3 access key.
2. Your Amazon S3 secret key.
3. The default expiration for all your expiring links. Can be overriden in each single shortcode.
4. Your default S3 host. Can be overriden in each single shortcode.
5. Your default S3 bucket. Can be overriden in each single shortcode.