Babel 6, labeled loops, await non-Promise, version-aware JS loader/directives

• Implement version-aware in-process JS compiler so modules built with different versions of nodent can co-exist
• Implement wrapAwait option to allow for the await nonPromise edge-case enabled in the standard implementation
• Implement 'optionSets' for each use nodent directive and allow their specification in the package.json to avoid use unnecessary use of setDefaultCompileOptions() and the consequent dependency between code and environment.
• Implement labeled break and continue containing await
• Only suppress the automatic insertion of return undefined if a function uses async return or async throw. Other async functions now return undefined asynchronously if the run to completion.
• Fix error that mangled the declaration of a let statement under certain conditions
• Fix Babel 6 integration (with fast-async)