Support for additional S3 headers #86
Description
When putting files to S3 it sometimes makes sense to set some Cache-Control header for the file (especially if you're using cloudfront to distribute it later).
S3 supports it through x-amz-meta-Cache-Control header on PUT request (and there are a lot of other properties which can be set using these "meta" headers).
I'd like to know if imager is interested in supporting this type of functionality.
E.g. pushToS3 can be modified to take the options dictionary from s3Config. If this all sounds ok, I can create a pull request.