lambert_bisection_test
  Use bisection to estimate a solution to the lambert equation.

  F(0) = -5 (negative)
  F(2) = 9.77811 (positive)

  After 23 iterations:
  F(1.32672) = -1.19233e-06 (negative)
  F(1.32672) = 8.98288e-07 (positive)

  it <= itmax?  true
  |xn-xp| <= xtol?  true
  min(|f(xn)|,|f(xp)|) <= ftol?  true