Add ability to set s3 host and path. If these values are empty, then default back to original url.  Otherwise, the generated path should be //<host>/<path>/<filename>
Properly initialize settings.
Save file in bucket subfolder if path is specified.
Construct correct path to s3 asset
Allow asset host and path to be set from environment variables. Update readme and instructions.
Support S3 file (non-image) uploads.
Merge branch 'upload-file' into add-path-and-host-settings
Update s3 file upload to use path and host settings.
Merge branch 'upload-file'
Merge branch 'integration'