v0.2.4: Schema Evolution and Append Column

Support Schema Evolution via Append Column.

What's Changed

• [Notebook] fixes for notebook backing the blog post by @changhiskhan in #316
• [C++] Append column by @eddyxu in #299
• [Python] Append columns by @eddyxu in #318
• [Use column projection during update by @eddyxu in https://github.com//pull/322
• update to duckdb 0.6 by @changhiskhan in #312
• [Python] Support add column via Expression. by @eddyxu in #324
• [Python] Expose projection for append column by @eddyxu in #325
• [C++] Support column projection during add_columns via expression by @eddyxu in #326
• [Python] Pytorch Dataset uses Fragment instead of files and support versions by @eddyxu in #327
• [C++] Move writer API a private API by @eddyxu in #329
• [C++] Refectory Metadata class to eliminate protobuf reference. by @eddyxu in #328
• [C++] Performance profiling and improvement by @eddyxu in #333
• [C++] Upgrade lq cmd tool to be able to inspect new versioned format by @eddyxu in #334

Full Changelog: v0.2.3...v0.2.4