Pass scheme specific parameters as cell array. This will enabale constructDiffOps to be more general. In addition, allow for schemes returning function handles as diffOps, which is currently how non-linear schemes such as Burgers1d are implemented.

% Get the index of the points p within the tall array of points ps
function [I, ok] = pointIndex(p, ps)
    [ok, I] = ismember(p,  ps, 'rows');
end