added two cljs builds (for dev and production environments), the APP_ENV environment var allows to select which one the web pages will load; this same APP_ENV environment var is used to choose a Leiningen profile when starting the app with Foreman (see Procfile); added lein-cljsbuild hooks so that when when running Leiningen's default tasks (compile, clean, jar...), the appropriate lein-cljsbuild taks are also run (this way there's no need to include compiled .js code in the repo, it will be built by Leiningen when required, in the same way that Clojure code is compiled to JVM bytecode when required); added wrap-reload middleware in the development environment so that modified namespaces are automatically reloaded on each namespace (for interactive development); removed trampoline when starting the app through Foreman due to a bug in lein-cljsbuild
added APP_ENV to example configuration in README