Add option to change base_point and base_sheets.

By default, a base_point and an ordering of the base_sheets is chosen
by monodromy following the method of Frauendiener, et. al. The
option to provide a base_point is added so as to better compare the
output of monodromy() to that of Maple's.
Add monodromy tests to test suite.
Fix branch point comparison tool.

In the case when two or more branch points are colinear with the base
point of the monodromy group the branch points closest to the base
point occur "before" those further away. This fix produces monodromy
group matching those of Maple. (When using the same base point and
base sheets ordering.)
Improve RiemannSurfacePath differential plot layout.

Rearrange subplots in RiemannSurfacePath.plot_differential so that the
value of the differential is easier to see next to the path, itself.
Add change of base point to RiemannSurface and homology.

We already added the ability to change the base point and ordering of
base sheets in monodromy(). Propogate those changes to homology() and
RiemannSurface.
Fine tune RiemannSurfacePath plotting.
Fix infinity path bug.

The positive direction around infinity is a circle around the fininte
branch points in teh negative direction. A sign error abou this
property was resolved.

Now, f2 produces a period matrix. It's still not confirmed whether
or not this period matrix is a period matrix of f2 but it at least
satisfies the properties of a Riemann matrix.

f10 is being tested but, unfortunately, does not produce a valid period
matrix.