WIP: Feature/convenient mpi

Hi, we propose here a more convenient interface to MPI, which implements the following features:

• non-blocking communications using future-concept (oriented at std::future)
• supporting exceptions
  • MPIErrors are treat by exceptions
  • extending existing MPIGuard capabilities
  • using ULFM if available
  • fallback to blackchannel approach, which is used to propagate an error state through the communicator and prevent deadlocks.
• resource management for MPI_Comm
• Datatypes
  • communication of dynamic datatypes that are stored in consecutive memory (e.g. std::vector)
  • MPIPack represents MPI_Pack. It can collocate objects of different types and send it within a single statement.
• Point to point communication (blocking and nonblocking)
• Collective communication (blocking and non-blocking)
• Low-level wrapper for MPI_IO (File IO)
• Low-level wrapper for MPI_Win (Remote memory access)
• high-level methods
  • Generic ring communication
  • NeighborIndexMapping construction

Sometimes we where a little bit rough when remove old interfaces. E.g.

• CollectiveCommunication<MPI_Comm>
• GuardCommunicator

Whats you opinion?

TODO

• Threading support
• replace wait[all|some|any] methods with when_all and when_any and group the Futures, s.t. MPI_Wait[all|some|any] can be used for Futures that provide a MPI_Request.
• overhaul naming (use CamelCase)