Simple readline like functionality

These are self contained OCaml bindings to linenoise, no system libraries needed at all.

Here's the simplest program:

let rec user_input prompt cb = match LNoise.linenoise prompt with | None -> () | Some v -> cb v;

user_input prompt cb

let () = (fun from_user -> Printf.sprintf "Got: %s" from_user |> print_endline) |> user_input "test_program> "

and compile with: $ ocamlfind ocamlopt ex.ml -package linenoise -linkpkg -o T