changelog: Add entry about rename of result::raw()
## [6.3.0] - unreleased
+- Changed: [[#293](https://github.com/ethereum/evmc/pull/293)]
+ In C++ API `evmc::result::raw()` renamed to `evmc::result::release_raw()`.
- Fixed:
[[#261](https://github.com/ethereum/evmc/issues/261),
[#263](https://github.com/ethereum/evmc/pull/263)]
