output/risk: some cleanup and docs
output/risk: some cleanup and docs


Former-commit-id: ce8aaf6b24d6ed6513fe2e9082f5bf0f52849973 [formerly bed9a94d40120dd6820c26f4fed7513b398e5cc4]
Former-commit-id: 5a41604f56e0ca824589b130024f5e58b3a6e5c6
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine