All files available for building on CPU
Preprocessor macro FILE_IO introduced

* Use it to enable/disable file I/O
* Location in debug.h
Workaround in Xeon toolchain file due to bug in cmake
Integration of MPI_Comm_spawn started
Snapshot
Snapshot
Snapshot
Snapshot
Implementation finished but not working
Much debugging code for issue #2
Results correct
Implementation finished, yet to be tested.
Tested and correct results.
Code running and correct with fields and particles solver division:

* Particles solver spawns fields solver
* Data transfer (moments): particles solver -> fields solver
  - rhoc
  - rhons
  - J{x,y,z}h
* Data transfer (fields): fields solver -> particles solver
  - E{x,y,z}th
Merge pull request #1 from rinke/issue_2

Spawn fields solver with MPI_Comm_spawn