tolower() the S3 bucket name

[jamesabel]

Currently the S3 bucket that pyship uploads to uses the author and application strings verbatim. However, S3 requires that bucket names be lower case only. So, if the author or application names has any upper case letters, we'll get an InvalidBucketName error.

The easiest solution is probably to tolower() all strings used to access (create, write, read) the bucket name.