draw_triangle that draw a triangle.
Usage :
draw_triangle(
px = [x1, x2, x3], #the points x positions (must be a list)
py=[y1, y2, y3], # the points y positions (must be a list)
c = (r, v, b), # the color of the triangle
step = 1 ) # the step, must be higher or equal to 1 (for a full filling), if it is greater than one the triangle will be hatched.