Process killing

Merging this adds the following main features

• Improved documentation
• Python Assimilator (written without boost) allowing to write assimilators easily in python
  • Support for WRF
    • Slow MPI (gather data via FS if too many elements to be indexed by int as done in the most MPI implementations)
• Cleanup of docker containers
• Repair of CI and some test cases
  • Improved killing of melissa sub processes between local test case runs