Extended character support for s3 compatible backend

[zifeo]

#111 introduced a limitation on which character can be used in a bucket, however s3 compatible backend supports some of them (e.g. the suffix +segments is automatically created by swift for large objects). This makes s5cmd impossible to use.

ERROR "[REDCATED]": InvalidBucketName: The specified bucket is not valid. status code: 400, request id: [REDCATED], host id: [REDCATED]