Update name resolvers to avoid confusion

Name resolvers can either be specified in the form chemspider_name, cir_name, opsin_name or in the form name_by_cir, name_by_opsin, name_by_cir. Previously, the XML response from the NCI Chemical Identifier Resolver used the former, but it recently changed to use the latter. Hence the CIRpy documentation, examples and tests have been updated to match the change.