Saving and loading Comparer objects

I saved a comparer:

```python
cmp.save("test.comparer")
``` 

Then I tried loading it with:

```python
ms.load("test.comparer")
``` 

Which results in an error that it's not a valid zip file. I realized afterwards that it saves to a NetCDF file, which can be loaded via:
```python
ms.Comparer.load("test.comparer")
``` 
