Upgrading version to 1.3.7-dev
Improved the events comment.
Fixed the content type check.

Thanks tienshiao #33
The file is now the last parameter added.

#33
Added the possibility to define additional params.

#30
Added a preparingupload event which can be used to add additional data to each upload.

Closes #42, #30, #33
Decided to ditch the preparingupload event and stick with only a sending event.
Added downloads.
Upgrading version to 1.3.7
Merge tag 'v1.3.7'

Added the possibility to add parameters for each file upload.