Integer division being used when dividing two dimensionless quantities.

There are some surprising results when doing divisions with dimensionless quantities.

```
>>> from scimath.units.SI import *
>>> dimensionless / dimensionless
1
>>> type(dimensionless / dimensionless)

>>> dimensionless / (2*dimensionless)
0
```

I'd expect `float` and `0.5`, here.

I also find it surprising that a multiplication or division with a unitless result returns a scalar (int or float) rather than another `scimath.units.unit.unit` instance, but that's another issue.