Replaces shell script with python version for cross-platform support

[philipmat]

fixes #79 and closes #109

• provides option to only produce the urls: --urls-only / -y
• option to save urls to a file -save-url=/tmp/discogs.urls
• directory to save dump files to

% python get_latest_dumps.py ~/Dev/tmp/discogs   

Retrieving http://discogs-data.s3-us-west-2.amazonaws.com/data/2020/discogs_20200901_releases.xml.gz
...100%, 8440 MB, 2468 KB/s, 3501 seconds passed
Retrieving http://discogs-data.s3-us-west-2.amazonaws.com/data/2020/discogs_20200901_masters.xml.gz
...100%, 334 MB, 2511 KB/s, 136 seconds passed
Retrieving http://discogs-data.s3-us-west-2.amazonaws.com/data/2020/discogs_20200901_labels.xml.gz
...100%, 53 MB, 1800 KB/s, 30 seconds passed
Retrieving http://discogs-data.s3-us-west-2.amazonaws.com/data/2020/discogs_20200901_artists.xml.gz
...100%, 319 MB, 2539 KB/s, 128 seconds passed
Retrieving http://discogs-data.s3-us-west-2.amazonaws.com/data/2020/discogs_20200901_CHECKSUM.txt
..2111%, 0 MB, 84096 KB/s, 0 seconds passed

[philipmat]

Not sure about this anymore. Seems like a bash + a powershell script might work better