Added function for closed form.
Added relative error function

Functions takes an empty array and two arrays with solution plus an int
telling the length of the arrays. All arrays must be of same length.

The function finds the relative error and stores it in the last array.
Added relativeError.cpp
Can read files from commandline again
Fixed something.
Doing exercise C

Currently in the process of solving exercise C. Wrote an error analysis
function. It is now producing numbers, but the plot should be checked
so that we know whether or not it actually produces real results.
Still working on getting erroring to work

Branching out and comparing with logarithm instead since this method
requires so many steps.
Fixed error analysis

Algorithm for finding errors for different steps h now works. Instead of
calculating for each step n an interval is chosen with logarithm. This
leads to fewer points and a better analysis. Data can now be used to
make interesting error versus step length plot.

Interesting problem: Cant use more steps than 100 because get
segmentation fault 11. Yet works perfectly for smaller. Why?
Fixed error where same name in args made seg-faults.