Adding support for object metadata

[nominee1997]

Hi!

It would be very useful to have better support for object metadata. This would include:

• Ability to include metadata in a PUT request (via passing through headers like x-amz-meta-$var)
• GET request should include the metadata (similarly passing through headers like x-amz-meta-$var)
• Method for querying only this metadata should be added. This should be done similar to S3 by performing a HEAD request (preferably as HEAD /get?bucket=$bucket&key=$key or if this is problematic, then a special GET /head?bucket=$bucket&key=$key method, and also HEAD /$bucket/$key for transparent usage)