Generate test environment dynamically at test-time.

This uses an Austin REPL along with the `analyze-source` function from `cljs.repl` to generate the compiler environment. There's currently a `test_ns.cljs` file in `test-resources` which contains the minimal amount of code to allow porting of any tests that previously relied on the compiler dump file; we can use this to easily add new test cases as required.

Not sure if this is the best way of doing this but it seems to work pretty well - let me know what you think!