gen-stat format agnostic

When using gen-stat from a config yml file is needed to use the complete filename including file extension eg:

```
Lora[wght].ttf:
- name: Weight
tag: wght
values:
- name: Regular
value: 400
...
```
I think it will be cool if the extension can be ommited so the same config declaration can be used to patch CFF variable fonts.