changes (#518)

changelog.md

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+# 0.3.1
+
+- Many improvements to COM support including interface hierarchies. ([#448](https://github.com/microsoft/windows-rs/pull/448))
+- New COM helpers simplify common operations. ([#496](https://github.com/microsoft/windows-rs/pull/496))
+- New `CoString` type representing null-terminated UTF16 strings backed by the COM task allocator required by some Windows APIs. ([#514](https://github.com/microsoft/windows-rs/pull/514))
+- The `windows` crate is now dual-licensed under MIT or Apache. ([#476](https://github.com/microsoft/windows-rs/pull/476))
+- COM interface methods are now marked `unsafe`. ([#508](https://github.com/microsoft/windows-rs/pull/508))
+- Many new examples have been added to the [examples](https://github.com/microsoft/windows-rs/tree/master/examples) folder. ([#501](https://github.com/microsoft/windows-rs/pull/501))
+- Improvements to error handling and propagation support.
+- Improvements to numerics support.
+- Improvements to build time.
+- Other minor changes and fixes.