Support multiple sources via srcs

[hrenard]

Hi !

I got a package with multiple sources synced via a same tag that Nix can build it in a single simple derivation.
To use nix-update, I believe the use of subpackages is required which adds a little overhead.
Is there another way to do it ? Or does supporting srcs makes sense for this project ?

[SuperSandro2000]

It is probably not easy to add generic support for srcs but it can be easily done with an update script and some clever use of sed and maybe some comment. A sub package should not be required.