docs(CHANGELOG): update changelog

CHANGELOG.md

@@ -1,5 +1,49 @@
 # Changelog
 
+### v0.4.0
+
+Performance improvements and ability to efficiently queue jobs from JS.
+
+BREAKING CHANGES:
+
+- TypeScript:
+  - the ID of a job is a `string` (database `bigint`), we previously incorrectly stated it was a `number`.
+  - `Helpers` was renamed to `JobHelpers`
+  - `TaskOptions` was renamed to `TaskSpec`
+- `queue_name` is now nullable (leave it null for maximum parallel performance)
+- when a job is modified using a `job_key`, the `queue_name` attribute is now reset like the other attributes
+
+WARNINGS:
+
+- The database schema has changed; your code should not depend on the database schema, only on the public interfaces (`add_job`, `remove_job`, etc), so this shouldn't be an issue.
+
+New features:
+
+- Significantly enhanced performance
+  - Changes database schema such that a job_queue record is only added/checked when necessary
+  - Uses prepared statements
+  - Can override the PostgreSQL pool size on the CLI (via `--max-pool-size`)
+- Dedicated API for queueing jobs from JavaScript/TypeScript (`makeWorkerUtils` / `quickAddJob`; @mrmurphy, @benjie #60)
+- `--once` now respects `--jobs`, so it can run jobs in parallel
+- `jobKey` is now available via TypeScript API (@tim-field, #78)
+
+Other:
+
+- Overhauled the `perfTest` script
+- Upgraded dependencies
+
+### v0.3.0-rc.0
+
+v0.3.0-rc.0 was never released as v0.3.0 because we jumped to v0.4.0 too soon.
+
+New features:
+
+- `job_key` enables existing jobs to be updated and deleted; can also be used for de-duplication (@gregplaysguitar, @benjie #63)
+
+Fixes:
+
+- Fixes `runner.stop()` (@MarkCBall, #66)
+
 ### v0.2.0
 
 BREAKING CHANGES: