Release v0.4.0-beta.4

Cool new features for this 0.4.0 version, which if everything is working, will soon go out :D

• Rework commands: they are now friendlier and accept different arguments depending on the command (check out documentation for more)
• Added support for referencing variables in env sections and environment variables (go to Tasks documentation to see more)
• Tasks can receive settings for when the result is being uploaded to the cloud. At the moment, the only option available is to ignore the file/folder so it won't upload (go to the Tasks documentation too)
• Start publishing the tool in PyPi: go and install it using pip install mdbackup 😄

And also some fixes:

• Fixed issues when uploading files to S3/B2 that will contain duplicated prefix keys or rogue / characters
• Fixed crash when using python 3.6 (we want to make it fully compatible with that version)
• Fixed failure when running a command using string as parameter