Added batch wrapper to support cmd.exe, slight powershell rework

[rubin55]

Hi Shyiko,

Here is a pull request with a batch script that makes it possible to use jabba from a regular cmd.exe.

I additionally did a small change on install.ps1 to unhinge jabba.ps1 from it, and make it a little bit more conforming to PowerShell's way of doing things. The installer now fetches the ps1 script from the matching release version. It does the same for the batch script.

Finally, I updated the install message which now mentions the batch script and a user can choose to add it to their path in one way or the other.

[shyiko]

@rubin55 Outstanding! Thank you so much for this! 🙇‍♂️

[rubin55]

Hey Shyiko, I just noticed I forgot the alias for Invoke-Jabba. The following needs to be added to jabba.ps1 so a user can type "jabba" instead of "Invoke-Jabba" :

Set-Alias jabba Invoke-Jabba

[shyiko]

@rubin55 🤝