~tieong/download-course

Added retries mechanism

Sometimes the server returns a 503, this Retry object ensures that we
don't give up immediately.

TODO: Wrap the GET/POST requests in try except block in case it fails even
with the retries, so that the script doesn't crash.
Updated output dir argument, set promotion arg to required
Updated README
Changed default path to the home directory
Updated README
Updated README
Updated Changelog
Updated README
Added some tests
Added workaround.

When the file doesn't point directly to the resource, try to go to the
page where it redirects and get the resource link.
Store the file_path instead of the file_name

To account for the case where files have the same name and in doing so
prevent them from being redownloaded every time the script is run.
Updated README
Removed selenium dependency
The user and the password now needs to be set in the env variables
Moved logging into init_config
Updated README,Changelog, and TODO
Added more logging
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