Draws a series of rectangles in the same way that rectangle does.
In some situations it can give a significant performance boost to use this function rather than calling rectangle separately for each rectangle.
verts should point to an array of
n_rects * 4 elements. Each group of 4 values corresponds
to the parameters x1, y1, x2, and y2, and have the same meaning as in rectangle.
an array of vertices
number of rectangles to draw