Simple Multibar: Render images with multiple types of bar chart

This class can be used to render images with multiple types of bar chart.

It can take sets of data with values to render bars in images that represent each value.

Currently it can render simple bar charts (data from one dimension array), compound bar charts (data from two dimensions array). It can also stack several bars in one.

The resulting bar chart image is served as the current script output in a PNG image of given dimensions.