Option to animate the drawing of the graph

Options added:
 - animate (boolean) - flag on whether to animate or not
 - duration (number) - duration of the animation
 - easing (string) - one of Raphael's supported easing options

 Methods changed:
 - drawSeries - added animation code

Method added:
 - seriesAverage - caculates the average y value for a set of coords

 NB diff fixed, minified js not modified