Options for printing the configuration

[raphael-proust]

Instead of having their configuration files tempered with, some users (e.g., me) would prefer to have user-setup spit out the configuration lines on stdout. These can be added easily to existing configuration file manually.

How about opam user-setup print which would print the different additions it would make with opam user-setup install?

This combines with opam user-setup print --editor=foo to print only the configuration for one editor.