First commit of branch performance:

Bugs fixed:
- Solved an issue with particles being injected with infinite velocity
  resulting in Inf velocity in some cells of the output files.
- Particles are now equally distributed in cylindrical geometry along
  the radial direction.

New features:
- Particles now have their own weight that is recalculated when the
  particle moves to a new cell. This avoid the reduction of density at
  r = 0.

Cases:
- Added a case of Argon flow around a cylinder to measure performance
  and future improvements.

src/modules/moduleSpecies.f95

@@ -34,6 +34,7 @@ MODULE moduleSpecies
     INTEGER:: e_p !Index of element in which the particle is located
     REAL(8):: xLog(1:2) !Logical coordinates of particle in element e_p.
     LOGICAL:: n_in !Flag that indicates if a particle is in the domain
+    REAL(8):: weight=0.D0
 
   END TYPE particle