Make target to install miscellaneous non-binary files

[JamiKettunen]

A separate e.g. installmisc target for non-binary files (which install depends on) would be nice so it can be called separately from e.g. the Void package build template where (cross-)building Go packages is handled with a build-style and a corresponding environment, and for non-binaries just this would be then needed:

post_install() {
    make PREFIX=/usr DESTDIR=${DESTDIR} installmisc
}

I previously sent https://lists.sr.ht/~craftyguy/superd/patches/36158 which the Void package handles in a similar way.

Copied mostly from #46 as I didn't get any particular feedback to this suggestion yet.

[JamiKettunen]

I suppose for now it's a bit redundant (at least in case of Void) as the same can be accomplished pretty easily also with:

post_install() {
    vcompletion scripts/completion/bash bash
    vcompletion scripts/completion/zsh zsh
}

Just thinking in terms of future additions it might become more complicated to keep maintaining.

[Elara6331]

Done in 8a1d0f4, thanks