Adding helper script for Ising model

Added a helper script for the Ising model to plot the magnetization as a function of the MC index
(analogous to "time").

Added Lectures 30, 31, 32

Added Lectures 30, 31, and 32 for Probabilistic Methods.

Added Lecture 28 cpp implementation

The Lecture28 implementation was still based on gnuplot instead of pyplot, updated now.

Adding Lectures 28 and 29

Adding Lectures 28 and 29 which solve parabolic and hyperbolic PDEs.

Adding Lecture 27

Adding Lecture 27 which demonstrates solution to Poisson's equation using multigrid methods.

Adding Lecture24, Lecture25 and Lecture26

I've added Lectures :
24 : boundary-value problems
25 : boundary-value problems
26 : PDEs

Added Lecture 22

I've added Lecture 22 on Celestial Mechanics.

Version 1.10 : Adding Lecture 21

Adding Lecture 21 to demonstrate ODE's and chaotic dynamical systems.

Version 1.9

Example code for Lecture 20, which starts off introducing ODE's. Uses a pendulum
and a baseball pitcher as starting examples.

Version 1.8

Added the NaCl example for Na2Cl2, in both C++ and python.