gf-3.12: CHANGELOG.md

### New since 3.12 (WIP)

### 3.12
See <https://www.grammaticalframework.org/download/release-3.12.html>

### 3.11

See <https://www.grammaticalframework.org/download/release-3.11.html>

### 3.10

See <https://www.grammaticalframework.org/download/release-3.10.html>