wrong error when not loading module inside a instance of repl

Hi! first of all, thanks for this project! I integrated on my neovim repl plugin mostly to be able to do autocomplete without everything breaking and it worked just fine!

The issue I first had (which I was able to solve by trial and error) is that if you do smth like (require :repl-protocol) inside a file and then run that file from the command line I would get an error of unsupported fennel version (which I knew it wasn't the case since I have fennel 1.3.1).

The actual issue is that since I wasn't running that require call inside an instance of a repl, ___repl___ doesn't exist, which I think is what the module checks to see if one can run the repl.

So, maybe the module should give a different error if the version is correct but is not loaded inside a repl environment?

Another, sort of, issue with this is that to define a format function I have to send it as a string to the repl process the same way I'm loading the proto-repl.

So, for now I'm doing repl.send "((require :protorepl) (fn [env data] data))")), where the format function just returns the table as is and then I intercept every output of the repl and then format in a way that is useful for me (basically turning sequential tables to associative tables).

This is just an inconvenience that also spans from the fact that I don't know how to serialize a function as a string using the fennel module (I don't know if there's a way for that, maybe not?)

Anyways, thanks!