Fixed some errors found by a sphinx build via "make html".
Fixed some errors found by a sphinx build via "make html".

gem/oq-engine,gem/oq-engine,vup1120/oq-hazardlib,gem/oq-hazardlib,gem/oq-engine,gem/oq-hazardlib,vup1120/oq-hazardlib,gem/oq-engine,gem/oq-hazardlib,vup1120/oq-hazardlib,rcgee/oq-hazardlib,gem/oq-engine,rcgee/oq-hazardlib