Adding extra package importers

[pinoaffe]

Hi guix,

Recently, I made an effort to get the guix-npm binary importer working
in combination with a relatively "modern" guix - my changes are rather
hacky and I think I may have broken a thing or two, but i got it to work
reasonably well in the REPL.
(many thanks to Jelle Licht and possibly others who initially wrote the 
importer)

Considering that such a binary importer is probably not well-suited for
inclusion in guix-proper, I would like to make it available through an
additional channel, mostly for my own use but maybe also for others.

However, the commandline interface for ~guix import~ operates based on a
list of importers in (guix scripts import) in guix proper - is there a
way to replace this functionality so that additional guix channels could
"extend" the list of importers?

Additionally, does anyone have an idea as to how to deal with the fact
that a single recursive import will often add several versions of the
same package? The only thing I could come up with would be to always
append the full package version to variable names, but that seems like a
somewhat ugly fix.

My current version of the code can be seen at
https://git.pixie.town/pinoaffe/guix-npm-binary

Kind regards,
pinoaffe