Add JS Plugin API reference page

Summary: This documents all pretty much the entire API.

Reviewed By: passy

Differential Revision: D15187834

fbshipit-source-id: 073c6a0dc40e3373967e9e5c5b7d44ab9c0aa07f

website/i18n/en.json

@@ -31,6 +31,9 @@
       "extending/index": {
         "title": "Clients and Plugins"
       },
+      "extending/js-plugin-api": {
+        "title": "JavaScript Plugin API"
+      },
       "extending/js-setup": {
         "title": "JavaScript Plugin Definition"
       },
@@ -55,9 +58,6 @@
       "extending/testing": {
         "title": "Testing"
       },
-      "extending/writing-a-plugin": {
-        "title": "Writing a plugin in JavaScript"
-      },
       "features/crash-reporter-plugin": {
         "title": "Crash Reporter"
       },