#8 Create canonical-sexp via constructors

Dear maintainers,

Would you be open to accept constructor functions for constructing canonical-sexps in code? See https://lists.gnu.org/archive/html/guix-devel/2021-11/msg00102.html for some context;

Hi @jlicht!

I replied with skepticism at the time, but I do see how a thin procedure that builds the sexp for public keys etc. can be appealing. That could avoid basic issues due to malformed sexps.

So I'm open to such an addition!

PS: Sorry for the one-year delay...