add bucket.GetKey to get metadata of a key
Infer the NextMarker if S3 didn't send it

Otherwise this only works if you specified a delimiter in the request.
The symptom is an infinite loop endlessly processing the exact set of
keys over and over again.
Merge pull request #39 from bobveznat/master

Infer the NextMarker if S3 didn't send it
Merge pull request #38 from nitrous-io/bucket-get-key

add bucket.GetKey to get metadata of a key
Add the support for "RequestSpotInstances" and "DescribeSpotInstanceRequests"
Merge pull request #41 from henrysher/add-spot-instance-support

add the support for spot instances