Draws the invoice header

def draw_header(canvas):
    """ Draws the invoice header """
    canvas.setStrokeColorRGB(0.9, 0.5, 0.2)
    canvas.setFillColorRGB(0.2, 0.2, 0.2)
    canvas.setFont('Helvetica', 16)
    canvas.drawString(18 * cm, -1 * cm, 'Invoice')
    canvas.drawInlineImage(settings.INV_LOGO, 1 * cm, -1 * cm, 250, 16)
    canvas.setLineWidth(4)
    canvas.line(0, -1.25 * cm, 21.7 * cm, -1.25 * cm)