API Doxygen: Collective

[ax3l]

Some of the public APIs still lack proper doxygen docs for their parameters.

Even more important, behaviour such as required collective calls (for the current MPI_Communicator) such as Series constructors/destructors, store/loadChunk, attribute writing, ... need be to mentioned in the respective method descriptions to avoid confusion.

[ax3l]

Collectives: started to be documented with #583