Unification of boundary conditions into one file.
Some changes to input file for reference cases. This should have been
done in another branch but I wanto to commit to save progress and I
don't want to deal with tswitching branches right now, I'm very busy
watching Futurama.
A boundary condition for each species must be indicated in the case
file.
This opens the door to use boundary conditions with different parameters
(for example, a wall temperature, coefficients for reflection or
absorption...)
The examples included with the code have been updated accordently.
Maxwellian and Diract Delta distributions have been implemented.
The input for injection of particles should be rewritten to allow more
clear input file.
