add numpy to requirements

In trying to run the ./examples/cube.py, I got an error about trying to import numpy:

Traceback (most recent call last):
  File "legos.py", line 4, in <module>
    import vapory
  File "/Users/rdm/.virtualenvs/lego-construction/lib/python3.6/site-packages/vapory/__init__.py", line 4, in <module>
    from .vapory import *
  File "/Users/rdm/.virtualenvs/lego-construction/lib/python3.6/site-packages/vapory/vapory.py", line 4, in <module>
    from .io import render_povstring
  File "/Users/rdm/.virtualenvs/lego-construction/lib/python3.6/site-packages/vapory/io.py", line 11, in <module>
    import numpy
ModuleNotFoundError: No module named 'numpy'

I'm not entirely sure numpy is needed, but if it is, it should be listed in the setup.py.

Hi managed to solve by installing numpy through pip pip install numpy

Ah looks like the code has an except for an IOError but not for a ModuleNotFoundError. That should be fixed. Probably not a lot of people run into this problem since numpy is a very commonly used module.

This issue has been fixed. If you import the library without numpy it works but if you need numpy for the particular function only then will it stop you.