consider dropping Clojure (target only ClojureScript)

The engine was written for Clojure because that was what I was learning at the time, but it feels like 99% of the time a user of this library will want to target primarily or exclusively the browser, because who wants to install clojure and play from the terminal?

Even while the conditional code was reduced a lot, removing reader conditionals in the requires alone would improve the readability of the code a lot.

Also, the project will become simpler and development process easier; I imagine new opportunities for improvement will become apparent once we start targeting a single host.

Obviously, unit tests and a better development workflow (i.e. better hot reloading without having to restart the game, fix whatever makes the figwheel repl unresponsive from time to time, etc.).

If you are reading this and think dropping terminal support is a bad idea, please chime in!