Fix static field error

With this syntax Clojure thinks update-repl-env is a static field of a C# class, which is not the case.
Fix IllegalArgumentException error

ArgumentException is the CLR equivalent of JVM's IllegalArgumentException
Fix threading issue in REPL

Unity methods now work
Improve REPL interface in Unity
Make weird, messy progress
Deleted Assets/ClojureAssetPostprocessor.cs preparatory to merge
Merge branch 'upstream-master' into origin-master