Compatibility with alternatives to AWS S3

[ouun]

Is your enhancement related to a problem? Please describe.
Current version of the plugin is only compatible with AWS S3. Support for other providers which support the S3 API could be provided without much additions.

Describe the solution you'd like
Another option to set custom S3 upload endpoints would be very useful. HumanMade's S3-Uploads Plugin is a very flexible example.

Additional context
If you agree I would be happy to test it and to open a PR.

[jeffpaul]

@ouun this isn't something we're immediately looking to support so much as ensuring the existing S3 integration is secure and meets the functionality needs for media handling before we branch out to other providers.