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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.

Adding a unique ID to the temporary files was not enough to allow
multiple jackknives to run at the same time. The config file must also
be unique.

The new function replaces existing key-value pairs and adds non-existing
ones. It also considers sections.

The function for calculating the self-energy was renamed and split into
smaller subroutines. This makes future implementations of similar
functions easier.
A bug when calling the abinitiodga executable was also fixed.

This allows to run multiple Jackknives at the same time.

Also print the execution time