2D weighted histogram

Calculates 2D weighted histogram and plots in color

This function calculates a 2D, weighted histogram from:
(1) an Nx2 matrix of 2D data points
(2) an Nx1 vector of weights
(3) M_1x1 and M_2x1 grid vectors

There is an option to plot the histogram in color using the "bar3c" function (included). The coloring is specified by either:

(1) an RGB tensor of size M_1xM_2x3 or
(2) a Kx3 colormap matrix

This is useful for visualizing a weighted dataset in probabilistic algorithms like EM and the particle filter.