5.xx Redo the example 'expfitdemo' from section 5.8 Separable Least Squares
     from the book.
     (a) Fit the function y=beta_1*exp(-lambda_1*t)+beta_2*exp(-lambda_2*t) to the 21 observations mentioned in the section and report the values for beta_1, beta_2, lambda_1, and lambda_2.
     (b) Plot the figure 5.4
     (c) There is clearly one outliner in the observations, which is it? Remove the outliner form the observations and fit the function again and report the new values for beta_1, beta_2, lambda_1, and lambda_2 and compare these with those from (a) and discuss.