Making the name of the S3 backup directory configurable

[strayduy]

When the Mongo backups are uploaded to S3, they're stored under the "backups" directory in the configured S3 bucket (i.e. the path to each backup is BUCKET/backups/YYYY-MM-DD_hh-mm-ss.gz).

I updated the module to allow you to configure the name of the directory in S3, so you can set it to a value other than "backups."

The directory name is configurable through any of the following environment variables:

• S3_BACKUP_DIR
• S3_BACKUP_DIRNAME
• S3_BACKUP_DIR_NAME

The MAX_BACKUPS setting will respect the configured directory name, so it will only remove backups that match the given directory prefix.

My use case is that I have a single S3 bucket with hourly, daily, and monthly backups, and I wanted the directory names to reflect which type of backup was in each directory. I also have a different MAX_BACKUPS value for each type of backup.

[alexkravets]

Thanks a lot for this! Could you please add a passage to the README.md as well to keep documentation consistent, and add yourself to the end of the doc contributors section. Also bump gem version.

Thank you!

[strayduy]

Updated the README and incremented the gem version.

[alexkravets]

Thank you!