Support for relative input and output file paths

Currently the `Edit-DTWBeautifyScript` cmdlet doesn't support relative file paths.
As I sometimes have quite long paths to deal with, I would like to be able refer to the input and output file as:

```PowerShell
Edit-DTWBeautifyScript .\MySript.ps1 .\MySriptNew.ps1
```

Which is also common for cmdlets like `Get-Content .\MyFile.txt`.