Added genus() to singularities.py. (Untested.)

We can now compute the genus of an algebraic curve using
the delta invariants of its singularities. This function is
untested at the moment.
Improve initial mododromy computational time and performance.

Steps are taken to improve initial monodromy performance.
First, we use a numerical (multiprecise) root finding
command (sympy.mpmath.calculus.optimization.findroot) that
accepts initial guesses. Since the Taylor continuation is
computed anyway this provides a good guess for a root
finding algorithm. Second, more of the numerics is migrated
to using sympy.mpmath more fully.

A possible next step would be to implement this multiprecise
analytic continuation in C/Cython.
Merge branch 'master' of github.com:cswiercz/abelfunctions