Lebesgue Integral

To be written when properly understood.
* Wrote an article on simple functions already. Link to there, and maybe add some graphics there (of non-equal function value steps)
* Add graphics here of several examples/different types of functions.
This page is very helpful: Lebesgue Integral - graphical concept - Mathematics Stack Exchange. The crucial difference is equally spaced partition of the range instead of the domain? Seems like the representation of horizontal vs. vertical bars is wrong. Instead, both Riemann and Lebesgue are sums of vertical bars, but in Riemann the bars are of equal width, where in Lebesgue the function values at points in a bar is equally different between all bars.