int_error(fint::Function, a, b, p::Vector{uwreal})
Returns an `uwreal` with the values of
Computes the integral
``\int_a^b {\rm fint}(x; p)\, {\rm d}x``
and the errors the parameters `p[:]` and (optionally) the limits of the intgeral (`a`, `b`).
The errors in the parameters `p[:]` and (optionally) in the limits of the intgeral (`a`, `b`) are propagated to an error of the integral. The result is returned as an `uwreal`.