Make package installable

See merge request !1

Both setuptools' and distutils' setup() functions were used, which
is wrong: setuptools is built on top of distutuls and should be used
instead. Calling setup() twice lead to the fact that pip couldn't install
the package because of two egg-infos generated.

In addition, some formatting was done in setup.py.

IMPORTANT -> Fixed sign error in the capacitance matrix. It caused the solver to inverte the sign in the potential

Define type of region_ndtuple[region_name].index_of_mesh_points and region_ndtuple.index_of_closed_points elements to int by adding dtype=int. The lack of this was causing errors when trying to use index_of_mesh_points to acess mesh.points

Replace the internal rotate etc functions in Inhull by the external ones + fix the RegularPolygon class