(34S) Integration (using the double-exponential method)

[emece67]

Changes done (v1.2r and v1.2x).

Now the program:

1. Returns the computed result in X
2. Returns an estimation of the error in Y
3. Returns the integration limits in Z & T
4. Returns the upper integration limit in L
   

There's also a check around the estimated error used to distinguish between integrals that evaluate to 0 and those that evaluate to small numbers. Now, integrals suspected to be equal to 0 are reported as such, thus \(\int_{-\pi}^\pi \cos(x)dx\) will be evaluated to 0, but \(\int_{-\pi/2}^{\pi/2} 10^{-100}\cos(x)dx\) will be evaluated to \(2·10^{-100}\). Both computations will return and estimated error different from 0.

Regards.

Edited: removing the comment about ABCD remaining untouched.