Feature/578 prettier.io formatting (#585)

* Reformatted codebase using prettier.io (should not change functional behavior)
* Formatted README.md, added CONTRIBUTING.md, .prettierrc configuration file, and installed pre-commit hook

manifest.json

@@ -10,7 +10,7 @@
     "48": "icons/icon48.png",
     "128": "icons/icon128.png"
   },
-  "permissions": [ "activeTab", "storage" ],
+  "permissions": ["activeTab", "storage"],
   "options_page": "options.html",
   "browser_action": {
     "default_icon": {
@@ -20,9 +20,10 @@
     },
     "default_popup": "popup.html"
   },
-  "content_scripts": [{
+  "content_scripts": [
+    {
       "all_frames": true,
-      "matches": [ "http://*/*", "https://*/*", "file:///*" ],
+      "matches": ["http://*/*", "https://*/*", "file:///*"],
       "match_about_blank": true,
       "exclude_matches": [
         "https://plus.google.com/hangouts/*",
@@ -31,11 +32,9 @@
         "https://teamtreehouse.com/*",
         "http://www.hitbox.tv/*"
       ],
-      "css": [ "inject.css" ],
-      "js":  [ "inject.js" ]
+      "css": ["inject.css"],
+      "js": ["inject.js"]
     }
   ],
-  "web_accessible_resources": [
-    "inject.css", "shadow.css"
-  ]
+  "web_accessible_resources": ["inject.css", "shadow.css"]
 }