Release notes for agda2hs v1.2

Changes

See https://github.com/agda/agda2hs/issues?q=milestone%3A1.2+is%3Apr for the full list of changes.

Fixed issues

See https://github.com/agda/agda2hs/issues?q=milestone%3A1.2+is%3Aissue for the full list of fixed issues.