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jbktsang: release round 4 dev and train

Delete round2/submitted/all_submitted.json

Delete round2/attempted/all_attempted.json

Update round 2 and 3

Round 2 data without splits

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Republish Round 3 all data without splits

Delete round3 directory

Delete round2 directory

Update README.md

Update README.md

Update README.md

Update LICENSE

Fix Typo