Proper documentation generation

[SemenchenkoVitaliy]

If file has some class and function that returns an instance of this class then it should export not only function but also class itself. Otherwise, metadoc won't be able to generate documentation for this class. And documentation should be generated because it will be confusing to have docs for the function that returns the class instance but don't have documentation for that class. For example:

// Class description
class SomeClass {

  // constructor description
  constructor() {}

  // Method description
  method() {}
}

// Get SomeClass instance
// Returns: <SomeClass>
const getSomeClassInstance = () => new SomeClass();

module.exports = { getSomeClassInstance };

/cc @tshemsedinov @belochub @nechaido @lundibundi

Edit: Examples can be found here:

metasync
https://github.com/metarhia/metasync/blob/master/lib/chain.js
https://github.com/metarhia/metasync/blob/master/lib/collector.class.js
https://github.com/metarhia/metasync/blob/master/lib/collector.functor.js
https://github.com/metarhia/metasync/blob/master/lib/collector.js
https://github.com/metarhia/metasync/blob/master/lib/composition.js
https://github.com/metarhia/metasync/blob/master/lib/memoize.js
https://github.com/metarhia/metasync/blob/master/lib/queue.js

common
https://github.com/metarhia/common/blob/master/lib/cache.js
https://github.com/metarhia/common/blob/master/lib/events.js
https://github.com/metarhia/common/blob/master/lib/iterator.js

metaschema
https://github.com/metarhia/metaschema/blob/master/lib/schema.js

metalog
https://github.com/metarhia/metalog/blob/master/metalog.js