Allow subject to be passed in.

[colonelpopcorn]

Currently s3Touch allows you to simulate an s3 object event through SNS, but it doesn't use a lot of the features of SNS. I imagine this is because you want to simulate an S3 event rather than an SNS event. However, I'd like to be able to pass a lambda command string in via the subject line. Would it be okay to add some parameters in the createMessage/publishEvent functions to add a subject line to the SNS event? Default could be "s3touch".