agile: backlog consider renaming registrar in boost serialisation
agile: update create a single container of element in model
cpp: work on the path spec details implementation

- merge path spec details sub-workflow with main cpp workflow as its
  not really that big.
- make includes builder interface a path spec builder interface, since
  this simplifies the path details assembly process.
- implement path details activities with a simple type "function" that
  resolves an SML type into a formatter.