They catch the SystemExit and KeyboardInterrupt exceptions, which
usually nobody wants.

This is done by turning `correlation_axis` into a list.

The function for the generalized outer product is moved to the
Jackknife class. This allows to take the axis along which the covariance
and correlation is be calculated as an argument, instead of the whole
outer product function.

The main improvement was the use of mathjax to render mathmatical
formulas in a nice way.

Also print the execution time