RuntimeWarning about division by zero in HueSaturationValue

When computing the HSV value, there are four possibilities for a division by zero:

https://github.com/daavoo/pyntcloud/blob/100998b8ae9acd7d20adddc85b0d66f5e9f1e677/pyntcloud/scalar_fields/sf_rgb.py#L44-L56

While the resulting `nan` are handled and don't cause any problems, python still produces an annoying RuntimeWarning:

```
sf_rgb.py:44: RuntimeWarning: invalid value encountered in true_divide
H[idx] = 60 * (rgb[idx, 1] - rgb[idx, 2]) / MAX_MIN[idx]
```

This could be suppressed, e.g. by wrapping the relevant code
```python
with np.errstate(divide='ignore', invalid='ignore'):
```
I'm not sure if that's the best approach though.