2D PN Junction completed.

1. The kink was because of incorrectly validating correct code!
2. Added Electric Field countor plots.

Things remaining:
1. Threshold voltage computation of MOSFET.
   By sweepign over voltage ranges.
   Looks to be > 2V.
   Analytical verification may be required.

2. Analytical solving for PN Junction
   Potential and Electric Field Distribution
   For a Gaussian doping
   Approximately!.