Updated outer loop

Continued work on outer loop for calculating the phase equilibrium data
using N-R-iteration at each (T,V) coordinate.

The iteration scheme seems to work, but the N-R-iteration does not
converge - presumably because there is no step control. Relaxation
permits the iterations to continue longer, but does not solve the
underlying problem.

Thus:
- Step control should be implemented
- Trivial solutions should be checked
- If none of the above helps, the calculations of the Hessian and the
chemical potential should be verified