changelog: add some recent fixes

Author: davidhewitt

CHANGELOG.md

@@ -1,6 +1,9 @@
 # Changelog
 
 - Unreleased
+  - Support object arrays ([#216](https://github.com/PyO3/rust-numpy/pull/216))
+  - `PyArray::new` is now `unsafe`, as it produces uninitialized arrays ([#220](https://github.com/PyO3/rust-numpy/pull/220))
+  - Fix thread-safety in internal API globals ([#222](https://github.com/PyO3/rust-numpy/pull/222))
   - Make arrays produced via `IntoPyArray`, i.e. those owning Rust data, writeable ([#235](https://github.com/PyO3/rust-numpy/pull/235))
 
 - v0.15.0