Attempt to add closure compiler. Fail miserably.
Constructor annotations and extends.
Improve our externs for async.
Ensure externs are all properly exported.
Add missing cache error constructor and param annotations.
Annotate that Impromptu extends EventEmitter.
Remove reference to exports variable.
Correct cache inheritance annotations.
Make the arguments passed to caching classes explicit.
Mark _claimSetLock callback as optional.
Mark the repository options as optional.
Clarify the context passed to the global update method.
Remove closure-compat in favor of updating closure-npc.
Remove unneeded package.json externs.

This was fixed by allowing closure-npc to parse JSON files internally.
Add a generic externs file to support custom process.env keys.
Provide a type for data returned from the server.
Update closure-npc version.
Invert the closure used to define the global impromptu instance.
Add Grunt task to check types.