Why call os.system('clear') ?

In this line of code, you use a system call to clear the screen: https://github.com/snare/voltron/blob/d9fef0bb4073d434c54415d55a1b5da92cb84696/voltron/view.py#L270

However, I tested it on windows, and using blessed works just fine :

```python
term = blessed.Terminal()
print(term.clear)
```