added description of the output to piv_poisson.m. TODO: documentation, example, tutorial
created first function outside of piv_poission, called to get the list of txt files
before removing the unnecessary things from final matrix
first refactoring, removed unnecessary estimates of Reynolds stresses, etc. left only Poission equation. data is now in a structure, not a 3D matrix anymore
started working on the poisson equation, not finished, stumbling around RHS expression
added a new sophisticated choice of optimal lambda         % Automatic optimal lambda:
        % Ref: http://www.enm.bris.ac.uk/admin/courses/ANA&PDEs/pde-lect8.pdf
        tmpc = cos(pi/(31+1)) + cos(pi/(30+1));
        lambda = 4/(2+sqrt(4-tmpc^2));
refactored, shining new version of piv_poisson with clear inputs, outputs and help
merged the refactor into master
removed obsolete files
created simple test_piv_poisson.m demo and updated README.md with the command and the output