feat(core): Switch to Promises everywhere. Adopt Node v4 ES6 (#648)

* 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

Author: tmcw

.eslintrc

@@ -1,6 +1,12 @@
 {
   "root": true,
-  "parser": "espree",
+  "parser": "babel-eslint",
+  "parserOptions": {
+    "sourceType": "script"
+  },
+  "plugins": [
+    "flowtype"
+  ],
   "rules": {
     "space-in-parens": 2,
     "space-before-blocks": 2,
@@ -21,8 +27,8 @@
     "no-new": 2,
     "key-spacing": 2,
     "no-multi-spaces": 2,
-    "valid-jsdoc": 2,
     "brace-style": 2,
+    "object-shorthand": ["error", "always", { "avoidQuotes": true }],
     "no-throw-literal": 2,
     "no-self-compare": 2,
     "no-void": 2,
@@ -32,13 +38,15 @@
     "quotes": [2, "single"],
     "indent": [2, 2],
     "curly": 2,
+    "strict": [2, "global"],
     "no-shadow": 0,
-    "no-undef": 2
+    "no-undef": 2,
+    "flowtype/define-flow-type": 1,
+    "flowtype/use-flow-type": 1
   },
   "extends": "eslint:recommended",
   "env": {
     "node": true,
-    "es6": true,
-    "browser": true
+    "es6": true
   }
 }

.flowconfig

@@ -0,0 +1,12 @@
+[ignore]
+.*node_modules/.cache/.*
+.*node_modules/conventional-changelog-core/test/fixtures/.*
+.*/test/fixture/.*
+
+[include]
+
+[libs]
+declarations/
+
+[options]
+module.ignore_non_literal_requires=true