make it possible to include clojurers as a library

[erkkikeranen]

includes a lib.rs that provides public access to modules, for using clojurers as a crate.

cargo.toml

[dependencies]
rust_clojure = { git = "https://github.com/clojure-rs/ClojureRS" }

main.rs

extern crate rust_clojure;
use rust_clojure::repl::*;
...

let repl = Repl::default();