First version of the LU decomposition.

Started writing a program to solve the Poisson equation by using LU
decomposition. I've tried to use the function lu() in the armadillo
library, but so far I've had no success. Need to figure out how it works
first.
LU decomposition solver incomplete.

Wrote an incomplete LU decomposition solver. Must read into
how lu() in the Armadillo library works first.
test
LU decomposition solver incomplete.

Wrote an incomplete LU decomposition solver. Must read into
how lu() in the Armadillo library works first.
Added comments in the programs.

Also wrote a few Python scripts for plotting the relative
error.