Allow S3 File Metadata object to be passed in request

[mbruning24]

It would be awesome if we could supply our own list of metadata headers that would be sent using the [X-AMZ-META-*] headers in the http request. That way, if we have case-specific data that is useful for performing s3-generated lambda functions or SQS/SNS events (for example, data about the user uploading the file, etc) there is an easy way to add those extra data points to the object being uploaded.

The XHR object appears to allow additional headers, so I imagine it wouldn't be too hard to extend that capability to the Uploader object? Unless I've missed something...

Note I'm an idiot and completely worded my question like a dolt. So this is the edited version :)