Computes the (1-alpha) Bootstrap confidence interval from empirical bootstrap distribution of sample mean.
The lower and upper confidence bounds are the (B*alpha/2)-th and B * (1-alpha/2)-th ordered means, respectively. For B = 1000 and alpha = 0.05 these are the 25th and 975th ordered means.
Returns a quantile value of x.
The quantile is determined by the f, a fraction between 0 and 1. For example, to compute the value of the 75th percentile f should have the value 0.75.