Various fixes in mkrpa2.py:

    -- Changed regularisation parameter in interband contribution.
       Paradoxically, using a smaller value of epsilon (1e-3) gives
       poor accuracy. This is probably due to the features in the kernel
       being way too sharp.

    -- Use grid parameters in file names

    -- In testing routine, calculate the total charge

    -- Use dimensionless integration variables in RPA_inter.
       In retrospect, the advantage is not clear. It might help
       if I decide to accelerate this routine, though.

    -- Handling of [0, r[0]] interval in RPA_intra

    -- Overall, much better accuracy was now achieved. However,
       RPA_intra is way too slow, and I have to think of some
       method to accelerate it.