Implementing injection with current density

WARNING: This current denstiy will be multiplied by the reference
length, no the surface area that is being used for injection!

New units in the injection of particles 'Am2' to inject a density
current. Manual has been modified accordingly.

Reference parameters are now also printed in the case folder.

src/modules/mesh/moduleMeshBoundary.f90

@@ -147,7 +147,13 @@ MODULE moduleMeshBoundary
             ALLOCATE(newElectron)
             ALLOCATE(newIon)
 
-            newElectron%species => part%species
+            IF (ASSOCIATED(bound%electronSecondary)) THEN
+              newElectron%species => bound%electronSecondary
+
+            ELSE
+              newElectron%species => part%species
+
+            END IF
             newIon%species      => bound%species
 
             newElectron%v = v0 + (1.D0 + bound%deltaV*v0/NORM2(v0))