Discussion: Future of test setup

@marijnh and I discussed gathering improvements to the tests we want to see. That way, we only loose blameability once and possibly save a lot of work. So far, I found:

• Bump default JS version for tests or specify target version range for each test (#614)
• Run single test case (#346)
• Run tests against a different acorn version (@adrianheine)
• Re-organize tests by theme/construct (https://github.com/ternjs/acorn/pull/614#issuecomment-341565273)
• Make test definition more declarative (@marijnh)