Only update is_charge_density when explicitely given

See merge request !3

fix compatibility with scipy 1.8

See merge request !4

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