Add CHANGELOG entry
Changed: In `evmc_load_and_create()` the `error_code` is optional (can be `NULL`).
- Changed: [[#293](https://github.com/ethereum/evmc/pull/293)]
In C++ API `evmc::result::raw()` renamed to `evmc::result::release_raw()`.
+- Changed: [[#311](https://github.com/ethereum/evmc/pull/311)]
+ In `evmc_load_and_create()` the `error_code` is optional (can be `NULL`).
- Fixed:
[[#261](https://github.com/ethereum/evmc/issues/261),
[#263](https://github.com/ethereum/evmc/pull/263)]
