Support for 'writeable' dirs inside the squashed root

First I'd like to thank you very much for the very good init hook that you have written and which I find quite useful to my projects.
 
I had once written a similar thing but didn't take the time to put it on github and it was way messier than your version. So when I recently needed to prepare squashed system on a USB device again, instead of rewriting what I had once written and then lost, I searched and found your implementation of this idea.

It only lacks one thing, to my taste : I like to be able to bind directories on the block device (the USB key I'm booting from), so *outside* the squashfs, to some location inside it. I typically use that for /etc, which allows me to keep it writeable. So I took the liberty of forking your project to implement this very simple feature. I'd prefer to see it implemented in your version rather than making another PKGBUILD and have two very close AUR packages, but I'll do that if you think it really disturbs the harmony of what you've written.

Best regards,

Greygjhart