Update engine_api documentation
Update engine_api documentation


Former-commit-id: 3c364790f0225d80c07252083f74cb8f404c4282 [formerly 25f59cdf00a540cd7e7a9ffa36f5901a48fa8b3f]
Former-commit-id: 3d4cbd0006b4c683055c0dc08af2b1d0e81c0f64
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine