Part of chain complex kernel done.

Added a function that computes part of the kernel of the differential
$C^1(X) \to C^2(X)$ in the cohomology chain complex. This part consists
of the nullhomotopic train track paths around the singularities. The
other part will consist of elements of the form $x - \phi(x)$, since we
are computing the invariant cohomology with respect to $\phi$.
Second part of the chain complex kernel done.

Although it is not yet well tested, since the code cannot yet produce
interesting transition maps.