Add S3 Transfer Acceleration to AWS::S3::Bucket

[danielpops]

This addresses #832

Example output matches the spec at http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-s3-bucket-accelerateconfiguration.html

[phobologic]

I'd remove this, and instead write a custom validator here that does the acceleration_status_values:

def validate_acceleration_status(value):
    valid_status = ["Enabled", "Suspended"]
    if value not in valid_status:
        raise ValidationError("AccelerationStatus must be one of: %s", ", ".join(valid_status))
    return value

The benefit of this is that it will take into account non-string values, such as Functions like Ref() (say someone wanted to pass this as a Parameter, for example, that'd be a Ref).

Then you can just use that validator in place of basestring.

[phobologic]

Looks great, thanks!