Integration Schemes: include formatted table of results

Reproduced table 2.1[1] using the forward, backward and central integration
schemes written in python. These differentials are found by implementing
a discrete Taylor expansion of exp(-x) in this python script.

Forward: First order explicit
Backward:  First order implicit
Central: Second order implicit

Printed output:

      ---------------------------------------------------------
      |    Forward            Backward           Central      |
      ---------------------------------------------------------
      | 1.71828182846       0.632120558829      1.17520119364 |
      | 1.05170918076       0.95162581964      1.0016675002 |
      | 1.00501670842       0.995016625083      1.00001666675 |
      | 1.00050016671       0.999500166625      1.00000016667 |
      --------------------------------------------------------

Forgot to include column for step size...

[1] "Numerical Methods in Astrophysics" ISBN: 0-7503-0883-4
tidy up