Iam

Add UploadServerCertificate and DeleteServerCertificate methods plus tests
Might want to make this take some form of _Request_ struct as its params, so that if Amazon add any additional parameters the function signature wouldn't change? eg. like [here](https://github.com/goamz/goamz/blob/fd651a6fd902f8767c97376904ccdff0a6d032cc/cloudformation/cloudformation.go#L195-L208) in the `cloudformation` package