draw_heatmap            Function to draw a heatmap based on prepared
                        "display list" (dl)
heatmap.n2              Main heatmap function
heatmapFlex             Tools to Generate Flexible Heatmaps
prepare_heatmap_data2   Function to prepare data for a heatmap:
                        scaling, dendrograms, ...
zoom_heatmap            Function to zoom into an already drawn heatmap
