v0.2.7 Dataset Diff and Metrics computation, and Dataset Version Metadata

What's Changed

• create and update tarball for pets by @changhiskhan in #372
• [C++] Sanity check to verify column does not overlap when merging a new table by @eddyxu in #375
• update notebooks so s3 credentials are not required by @changhiskhan in #376
• Add function to get version as of a certain date. Also formatting by @changhiskhan in #378
• convenience for comparing metrics across versions by @changhiskhan in #379
• Changhiskhan/datadiff by @changhiskhan in #380
• Refactor dataset diff and compute metric by @changhiskhan in #381
• [C++] Attach new schema update when update dataset by @eddyxu in #374

Full Changelog: v0.2.6...v0.2.7