scripts/pull-latest-microg: refactorize; actually make reliable; rename

[sewnie]

Here you go. makes your script less terrible. I also refactorized the script because:

1. I do not like duplicated code
2. I do not like seeing parameters such as cURL --fail be unused
3. I do not like programs that have no mechanism to simply (note, simply, in bash, there is no goto) retry a request
4. I do not like resource intensive code.

I also notice that the rest of the module's code and other scripts are written terribly, but those are out of scope, since they work.

[becknik]

Thanks for your work - I can confirm it works fine :)