Bug: sheep-cli panics on input with globbing (Windows)

### Issue
When I specify the input files using globbing, sheep-cli crashes with
```
thread 'main' panicked at ' Failed to open image: IOError(Os { code: 123, kind: Other, message: "The filename, directory name, or volume label syntax is incorrect." })
```
I looked into it and found out that this is due to Windows not expanding input arguments using globbing.

### Possible Fix
Use glob crate to expand inputs with globbing.