The HTTP notifications are now invoked as POST and the notification is
a JSON inside the POST body.
This is a backward incompatible change but this way the actions can be
extended more easily, sorry for the trouble
Fixes#101
Please note that if the upload bandwidth between the SFTP client and
SFTPGo is greater than the upload bandwidth between SFTPGo and S3 then
the SFTP client have to wait for the upload of the last parts to S3
after it ends the file upload to SFTPGo, and it may time out.
Keep this in mind if you customize parts size and upload concurrency
