* for-of: IteratorClose spec compatibility.
See #3:
https://tc39.github.io/ecma262/#sec-iteratorclose
* Update spec fixtures for for-of.
* Fix IteratorClose case for remap-async-to-generator.
* Fix IteratorClose case for async-generator-function test output.
* Modify few tests according to iteratorClose fix.
* Fix iteratorClose for helpers.slicedToArray also.
* Update iteratorClose fixture for commonjs.
* Remove whitespace generation and rely on default printing
Changes to printing:
* Add newline after last empty SwitchCase
* Add newlines around block comments if they are non-flow comments or contain newlines
* Fix a few more fixtures
* Handle arrow function processing via shared API rather than default plugin.
* Fix a few small PR comments.
* Preserve existing spec arrow 'this' rewrites, and support spec in subclass constructors.
