Starts a dev loop using clojure.tools.namespace.repl/refresh in order to restart the app without
restarting the JVM.
Also starts an nrepl server which will keep up even between app crashes and restarts.

How to use:
lein run -m gdl.backends.libgdx.dev ~app-namespace~ ~app-fn-with-no-args~

Example:
lein run -m gdl.backends.libgdx.dev gdl.simple-test app

See also project.clj for the `lein dev` shortcut.

In case of an error, the console prints `WAITING FOR RESTART` and
the `/restart!` function will restart the app and call `refresh`.

You can bind this on a key for smooth dev experience, here in VIM:
``` vimscript
nmap <F5> :Eval (do (in-ns 'gdl.backends.libgdx.dev)(restart!))
```