Fixing session token

Adding support for session token

Version 0.7.1

Merge pull request #18 from Mixbook/add-generic-revisions

Add generic revisions (not timestamps)

Specify mime type when uploading objects to S3

Fix failing in Ruby 2.2.3

By some reason it worked fine in 2.1.2, but not in 2.2.3
It seems like importing of aws-sdk is messed up, so we need
to help it a bit by importing EndpointProvider manually

Add retry logic

Version 0.6.2

Version 0.6.1

Add parallel upload

Now we upload in 20 threads, it gets way faster with big projects.
Also, moved to aws-sdk official AWS SDK Ruby gem, because the old one
(aws-s3) was not thread-safe and worked incorrectly with parallel
uploads.