Enable pyArborio input routines to consume Stream objects in addition to files by name.
- NML
- NeuroLucida ASC
- SWC

Closes #1459 

PyArbor I/O routines now try to cast `filename` arguments to a string.
This allows passing `pathlib.Path` objects.

Example
```py
here = Path(__file__).parent
cat = A.load_catalogue(here / 'local-catalogue.so')
```