Migrate away from stack #191
Description
Currently cornelis depends on stack, which, as an abstraction over cabal, appears to be decreasing in popularity and support.
It would probably be best if we could depend only on cabal. Unfortunately, the nvim-hs plugin system that we use depends on nvim-hs.vim; whose entire job is to find the plugin executable in a hidden stack build directory and then execute it with the correct arguments.
Fixing would improve cornelis' stability but take a bit of work.