* feat(core): Switch to Promises everywhere. Adopt Node v4 ES6
Big changes:
* Uses template strings where appropriate
* Config and argument parsing is unified and there is no such thing
as formatterOptions anymore. All user-passed options go through
mergeConfig.
* The node API surface changed (again): `buildSync` is removed,
building operations return Promises.
* Now using Flow for internal type annotations.
More changes:
* Remove buildSync command
* feat(inference): Partially implement object shorthand support
* Refs #649
* Use Flow annotations to enforce types
* Keep flow but switch to comment syntax
* Clarify types
* More flow improvements
* Turn server into class
* LinkerStack becomes class too
* Fix comment description type
* Run flow on lint
* Many more flow fixes
* More intense flow refactoring
* Simplify inference steps
* Update inference tests, flow errors down to 1
* Continue refining types
* Fix more flow issues
* Use 'use strict' everywhere
* Make 'ast' property configurable
* Fix many tests
* Fix more tests
* Fix more tests
* Fix augments
* Test Markdown meta support
* Improve test coverage
* Switch back from for of to for for speed
