Allow to specify a customised password-store path

[galaunay]

This small PR allows the user to specify a customised password-store location.
Just in case people don't use the default "~/.password-store" location.

[DamienCassou]

Thank you for your PR. I like what you did and find this useful.

[DamienCassou]

Because this package is in Emacs core now, I need you to sign the FSF papers before I can merge your code. Is that ok?

[galaunay]

Thank you for the comments.
I defined the customisation group as a subgroup of auth-source.
Tell me if there is any other improvements to make.

No problem about the FSF papers, how are we supposed to proceed ?

[DamienCassou]

Good job. One minor thing left and I will merge.

[DamienCassou]

I defined the customisation group as a subgroup of auth-source.

that's great

No problem about the FSF papers, how are we supposed to proceed ?

I will merge your PR as it is small enough to be accepted even without the papers signed in my opinion. But please send a mail to assign@gnu.org and ask for the copyright assignment form.

[galaunay]

Thanks,
I removed the group and sent a mail to gnu.

[DamienCassou]

Great job, thank you. Can you please squash all your commits into just one before I merge?

[galaunay]

It should be clean now.

[DamienCassou]

Thank you very much

[galaunay]

Thank you for this package !