Installation with `pip`

[fnattino]

Thanks a lot for the very useful library!

I have faced an issue with the installation of morphsnakes using pip as described in the README file.

The issue is related to the dependencies of morphsnakes: numpy and scipy are not automatically installed when running pip install morphsnakes:

$ pip install morphsnakes
Collecting morphsnakes
  Using cached morphsnakes-2.0.1-py3-none-any.whl (7.8 kB). 
Installing collected packages: morphsnakes 
Successfully installed morphsnakes-2.0.1

so that when I try to import morphsnakes:

import morphsnakes

the following import error is raised:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/fnattino/Projects/Eratosthenes/Repos/morphsnakes/morphsnakes.py", line 56, in <module>
    import numpy as np
ModuleNotFoundError: No module named 'numpy'

I would be happy to help fixing this in order to use this tool as a dependency in a project package I am working on, so if you don't mind I will open a PR to address the issue!