Refactored so sectiondef.rst_nodes has consistent return signature
Refactored so sectiondef.rst_nodes has consistent return signature

All other rst_nodes methods return a list of nodes, whereas this
returned a list and the section kind. Another method has been added to
retrieve the section kind.

RR2DO2/breathe,kirbyfan64/breathe,RR2DO2/breathe,kirbyfan64/breathe,AnthonyTruchet/breathe,AnthonyTruchet/breathe,kirbyfan64/breathe,AnthonyTruchet/breathe,AnthonyTruchet/breathe,kirbyfan64/breathe