Onivim might not be for you :) But our project under the hood, libvim [1], might be useful for you to start (if it's easy to create bindings from C in Go).
There's a cool non-Onivim usage of it called Paravim [2] (and the same author also used it for Vim-Cubed [3])
Just to be clear, I was making my comment more in the context of vim than Onivim. I maybe should have said that originally, my bad. I backed Onivim and am keeping a close eye on it. Maybe I won't need to (try to) make my editor :)