New smoothing kernels for dgrid3d.
New smoothing algorithm for plot: 'smooth cumulative'
Updated documentation for dgrid3d.
Fixing two compiler warnings related to dgrid3d.
Demos for dgrid3d and smooth freq and smooth cumul.
Added log entry for new demos (dgrid3d and smooth cumul demos).
Changes for new smoothing algorithm for smooth histograms using Gaussian kernel density estimates.
Follow code conventions for new code on smooth kdensity.