Feature request: ability to change app name

[tecosaur]

Hello!

I've just started using this with Mu4e and mu4e-alert. Thanks for going to the effort to build such a handy library.

I know this may sound somewhat strange, but I'd really appreciate the ability to have the app name be another tweakable parameter. While strictly speaking the "app name" is of course emacs, in my DE: solus, (and I imagine I wouldn't be alone) this parameter seems to be used to sort notifications into per-app blocks.

In this respect, I would quite like to be able to use this to sort alerts from different parts of emacs, i.e. have mu4e in its own section in this example.

https://github.com/jwiegley/alert/blob/7046393272686c7a1a9b3e7f7b1d825d2e5250a6/alert.el#L728

Thanks for your work!

tecosaur.