ec2: Added DescribeImageAttribute API call
Allow custom headers for S3 Put

* S3.PutWithHeader & S3.PutReaderWithHeader
	* Take in custom headers instead of just Content-Type
	* Allow custom headers to override default set
		* Default to Content-Type: application/text
Merge pull request #13 from ZhangBanger/s3_put_headers

Allow custom headers for S3 Put
Update ec2.go

Updated comment to match AWS documentation:

http://docs.aws.amazon.com/AWSEC2/latest/APIReference/ApiReference-query-DescribeImages.html
Merge pull request #14 from brettweavnet/master

ec2: update comment to match AWS docs.
Merge pull request #10 from jmassara/DescribeImageAttribute

ec2: Added DescribeImageAttribute API call
updated tags to specify support for more than instances
Merge pull request #15 from brettweavnet/master

ec2: updated tags to specify support for more than instances