Upgrading version to 2.0.16-dev
Added the acceptedMimeTypes option.

Closes #121
The server error message is a dictionary now, and it provides the xhr object.

Closes #118
Changed file.previewTemplate to file.previewElement.

Kept file.previewTemplate for backwards compatibility.
Added all download files.
Upgrading version to 2.0.16 (file.previewTemplate is now file.previewElement and acceptParameter is now acceptedMimeTypes)
Merge tag 'v2.0.16'

file.previewTemplate is now file.previewElement and acceptParameter is now acceptedMimeTypes