Prepare for v0.4.0 (#513)

* update CHANGELOG

* tweaks

Author: yihozhang

CHANGELOG.md

@@ -2,6 +2,56 @@
 
 ## [Unreleased] - ReleaseDate
 
+## [0.4.0] - 2024-1-TODO
+
+Semantic change (BREAKING)
+
+- Split `function` into `constructor` and `functions` with merge functions. (#461)
+- Remove `:default` keyword. (#461)
+- Disallow lookup functions in the right hand side. (#461)
+- Remove `:on_merge`, `:cost`, and `:unextractable` from functions, require `:no-merge` (#485)
+
+Language features
+
+- Add multi-sets (#446, #454, #471)
+- Recursive datatypes with `datatype*` (#432)
+- Add `BigInt` and `BigRat` and move `Rational` to `egglog-experimental` (#457, #475, #499)
+
+Command-line interface and web demo
+
+- Display build info when in binary mode (#427)
+- Expose egglog CLI (#507, #510)
+- Add a new interactive visualizer (#426)
+- Disable build script for library builds (#467)
+
+Rust interface improvements
+
+- Make the type constraint system user-extensible (#509)
+- New extensible parser (#435, #450, #484, #489, #497, #498, #506)
+- Remove `Value::tag` when in release mode (#448)
+
+Extraction
+
+- Remove unused 'serde-1' attribute (#465)
+- Extract egraph-serialize features  (#466)
+- Expose extraction module publicly (#503)
+- Use `set-of` instead of `set-insert` for extraction result of sets. (#514)
+
+Bug fixes
+
+- Fix the behavior of i64 primitives on overflow (#502)
+- Fix memory blowup issue in `TermDag::to_string`
+- Fix the issue that rule names are ignored (#500)
+
+Cleanups and improvements
+
+- Allow disabling messages for performance (#492)
+- Determinize egglog (#438, #439)
+- Refactor sort extraction API (#495)
+- Add automated benchmarking to continuous integration (#443)
+- Improvements to performance of testing (#458)
+- Other small cleanups and improvements (#428, #429, #433, #434, #436, #437, #440, #442, #444, #445, #449, #453, #456, #469, #474, #477, #490, #491, #494, #501, #504, #508, #511)
+
 ## [0.3.0] - 2024-9-12
 
 Cleanups