More interesting vega plot

[sverhoeven]

The vega plot of epsilon versus duration is a bit disappointing. As changing the input has not much impact on the plot.

Some alternatives:

• plot root of different functions like x^3 - x^2 + 2, x^3 − 2x^2 − 11x + 12, x^3-2x +2 (does not converge when guess=0), x^2-1, −sin(x) − 3x^2, x^2 − 2, adjust code to pick one of functions, will also need derivatives of all those functions.
• plot number of iterations versus epsilon or guess, will need adjust code count them first