DuckDB: 0.3.1 Preview Release "Spectabilis"

This preview release of DuckDB is named "Spectabilis" after the [King Eider](https://en.wikipedia.org/wiki/King_eider) Binary builds are listed below. Feedback is very welcome. Note: Again, this release introduces a backwards-incompatible change to the on-disk storage format. We suggest you use the EXPORT DATABASE command with the old version followed by IMPORT DATABASE with the new version to migrate your data. See the [documentation](https://duckdb.org/docs/sql/statements/export) for details. Below a list of changes in this release **Features** - #2393: Switch to Push-Based Execution Model - #2417: Add support for GROUPING SETS, ROLLUP, CUBE and GROUPING/GROUPING_ID - #2347: Support for ENUM Types & #2404: Native mapping between R factors and DuckDB ENUMs - #2419: Allow WHERE clause referring aliases defined in SELECT clause - #2473: Adding Compression Option for Column Definitions to SQL Parser - #2489: Implement MAD (Moving Absolute Deviation) Aggregate - #2520: Add LIST_CONCAT and LIST_APPEND functions - #2522: MSD (Most Significant Digit) Radix Sort - #2529: Implement REGEXP_EXTRACT - #2482: Add support for EVEN - #2555: Adding BINARY_AS_STRING parameter to the parquet scan **Minor Changes & Bug Fixes** - #2377: Fix current_schema() and current_schemas() - #2380: Add tests for "did you mean" error message - #2381: Let FTS index creation respect the current schema. - #2382: Dropping support to Python 2 - #2385: BLOB support for JDBC - #2389: Replace __getattr__ on PyBind11 classes with individual properties. - #2390: Moving big categorical tests to tests_slow folder - #2394: Add SET s3_endpoint support for in-house Ceph - #2397: Add Python .pyi stubs - #2402: GH Actions Upload: retry asset upload with timeout - #2403: Not altering original DF when renaming columns in the binder - #2405: Fix bug with enum::varchar cast on null values - #2408: Rewrite Arrow table register for R using replacement scans - #2409: Adding dependency on Enum Types -> Tables - #2412: Updated src readme to state we use push-based execution. - #2413: Fix for #2411 - #2421: Fix #2407: use correct template parameters for DATE in arg_min/arg_max - #2423: Fix #2416: fix binding issues related to binding parameters, null values, etc in list_extract and array_length - #2424: Issue #2388: QUANTILE_DISC for VARCHAR - #2430: Fix for #2426 - #2431: More fixes for #2416 - #2434: Issue #2388: Moving VARCHAR QUANTILE_DISC - #2437: implement GEN_RANDOM_UUID - #2438: Issue #2432: PERCENTILE_XXXX ignores DESC - #2439: fix: pass absolute path to `System.load()` in Java - #2444: Fix #2440: correctly report run-time errors in Python client - #2445: Several OSS Fuzz Fixes - #2448: Move to codecov v2, and use add_library for vector operations for low RAM machines - #2449: Enum to Enum Comparisons - #2451: Hooold the loooock for Python Strings under Dataframe Object Columns - #2453: Fix when getting single values from ENUMs - #2455: Doc Improve: Trying to Update doc in `QueryResult` - #2456: Add --test-dir parameter to unittest so we can test out-of-tree extensions with it - #2462: Fix #2452: Implement Coalesce instead of rewriting to CASE chain - #2463: More OSS Fuzz fixes - #2474: Allow Fetch of chunks containing a multiple of vector sizes for the Arrow Record Batch Reader - #2476: Really holding the lock this time - #2477: Sorted aggregate: only re-order when ordering count > 0 - #2485: Benchmarks: Handle comparisons for values that do not have a VARCHAR ->TYPE cast (e.g. complex/list types) - #2487: Conditionally define UNLIKELY in Thrift - #2488: ODBC: fetching the first chunk in SQLExecute - #2490: Clean up RadixSort code - #2491: These tests are now passing with arrow 6 - #2494: Emit full vectors from VALUES lists instead of emitting individual tuples - #2497: Upgrade Catch to v2.13.7 - #2500: Fix nested string order - #2501: Add CIFuzz action - #2503: Fix for py string conversion on large strings - #2504: More precision for `SUM` and `AVG` - #2517: Move Kahan sum to separate method (fsum, sum_kahan) - #2521: Issue #2515: Windowed quantile list - #2527: testing: Add oss-fuzz fuzzer - #2536: Fix #2518: in read_csv_auto don't override names if names have been provided - #2537: Fix #2531: in recursive CTE avoid waiting for events to finish if an event has thrown an error - #2539: Restructuring CI Workflow - #2542: Issue #2530: Reset windowed lists - #2550: ODBC: Running PSQLODBC tests on Win64 - #2556: Fixed directory separator bug - #2558: Fixing positional reference binding in ORDER BY clause - #2559: Issue #2552: General ordered aggregates - #2561: Fix master CI: Python workflow needs auth tokens for deployment - #2563: Move ExtensionHelper into main DuckDB Class - #2564: R Client: Moving UTF encoding to R to avoid multithreading issues - #2567: Fix #2538: crash in CSV auto-detect when reading ZSTD data - #2573: Move HTTPFS builds to separate test to avoid deploying them by default on Linux - #2574: Naming optimizer-created aggregates so plans are interpretable - #2579: Support to Arrow 6 - #2580: Check magic bytes before checksum when opening a DuckDB database file - #2585: Fix #2584: correctly handle edge cases for bigger than 1 increments in range table function - #2587: Replacement Scans for Arrow Objects - #2592: Fix #2577: Rework case statement to avoid rewrite into nested binary cases - #2593: Fix #2591: avoid using ungrouped aggregate for non-combineable aggregates - #2594: Fix #2588: timestamp -> date cast is not invertible - #2595: Fix #2543: case insensitive replacement scans - #2598: OSS Fuzz Fixes - #2603: The asset upload script for releases was broken somehow - #2605: Clean up reupload by splitting it into two functions - #2604: Fix #2599: maintain correct dependencies between UNION ALL nodes so that output is deterministic/in-line with what a sequential execution would produce