Add changelog for v4.0.0 release (#633)

* Prepare for v4.0.0 release

* changelog notes for v4.0.0

* update release date

CHANGELOG.md

@@ -7,6 +7,37 @@ The public API of this library consists of the functions declared in file
 
 ## [Unreleased]
 
+## [4.0.0] - 2022-08-23
+### Breaking changes
+- Rename functions according to the terminology RFC (#622, #586, #571, #403, #466, #495, #466)
+- Functions that can experience errors now have an `H3Error` return value. (#617, #586, #581, #551, #550, #509, #505, #507, #508, #503, #478, #468, #436, #359)
+- Cell count parameters use `int64_t` instead of `int`.
+- `polygonToCells` (previously `polyfill`) accepts a flags argument for future expansion. (#570)
+- `cellToLocalIj` and `localIjToCell` accept a mode argument for future expansion. (#586)
+- `exactEdgeLength` functions renamed to `edgeLength` (#639)
+
+### Fixed
+- Fix polyfill bug when vertex latitude exactly matches cell center. (#603)
+- A number of issues detected via unit tests and fuzzers were fixed. (#568, #562, #558, #559, #560, #430)
+- `polygonToCells` returns an error if Infinity is passed in. (#636)
+
+### Changed
+- The file `CMakeTests.cmake` is no longer included if `ENABLE_TESTING` is off. (#609)
+
+### Added
+- Vertex mode and associated functions: (#422, #420, #417)
+    - `cellToVertex(cell, vertexNum)`
+    - `cellToVertexes(cell, out)`
+    - `vertexToLatLng(vertex, out)`
+    - `isValidVertex(vertex)`
+- `h3` CLI application. (#556, #497)
+
+### Other changes
+- Generally use `lng` instead of `lon`
+- Closed-form implementation of `numHexagons`
+- A number of fuzzer harnesses are now included in the H3 core library. (#557, #553, #545, #433)
+- Additional benchmarks are added and benchmarks are regularly run in CI. (#524, #518)
+
 ## [4.0.0-rc5] - 2022-08-16
 ### Breaking changes
 - `exactEdgeLength` functions renamed to `edgeLength` (#639)

VERSION

@@ -1 +1 @@
-4.0.0-rc5
+4.0.0