Generate docs from src, publish to gh-pages

Fix any broken JSDoc syntax. Unfortunately there is no way to document tuples like `{[int, int]}` for a `[width, height]` array. We could possibly fix this and make the code more readable with `{width: number, height: number}` instead of tuples.

Remove single `@fileoverview` from Rectangle.js, since it was the only file with one and was weird to have that one module show up on the docs home page.

Add a `docs` script to `package.json`, run it from `npm test`, so invalid docs will cause tests to fail (eventually we may want to start using eslint-plugin-jsdoc to catch these errors with the linter alone).

.jsdoc.json

@@ -0,0 +1,20 @@
+{
+    "plugins": ["plugins/markdown"],
+    "templates": {
+        "default": {
+            "includeDate": false,
+            "outputSourceFiles": false
+        }
+    },
+    "source": {
+        "include": ["src"]
+    },
+    "opts": {
+        "destination": "playground/docs",
+        "pedantic": true,
+        "private": true,
+        "readme": "README.md",
+        "recurse": true,
+        "template": "node_modules/docdash"
+    }
+}