Added comments
Finished subroutine send_particles (Alban)
First attempt at update_particles
attemp at merging conflict
Update particle positions for case leaving cube
Added comments
Add init_xv_test for testing purposes.
Merge changes between subroutines send and update
Merge branch 'master' into group2
Debugged version1.
finished kernel initialization
Merging conflicts from kernel work
Merge branch 'group2'