(chore) Add ESLint config and clean up the major stuff (#2503)

* (chore) eslint:recommended
* (chore): eslint_standard
* relax eslint rules for language grammars (to discourage rewriting them in one fell swoop; I'd rather have the blame history intact)
* remove extra escaping
* clean up variables
* more camelcase

.eslintrc.js

@@ -0,0 +1,56 @@
+module.exports = {
+    "env": {
+        "browser": true,
+        "es6": true,
+        "node": true
+    },
+    "extends": [
+        "eslint:recommended",
+        "standard"
+    ],
+    "globals": {
+        "Atomics": "readonly",
+        "SharedArrayBuffer": "readonly"
+    },
+    "parserOptions": {
+        "ecmaVersion": 2018,
+        "sourceType": "module"
+    },
+    "rules": {
+      "array-callback-return": "error",
+      "block-scoped-var": "error",
+      // we like our semi-colons
+      "semi": ["error","always"],
+      // our codebase doesn't do this at all, so disabled for now
+      "space-before-function-paren": ["error","never"],
+      // for now ignore diff between types of quoting
+      "quotes": "off",
+      // this is the style we are already using
+      "operator-linebreak": ["error","after", { "overrides": { "?": "after", ":": "after" } }],
+      // sometimes we declare variables with extra spacing
+      "indent": ["error", 2, {"VariableDeclarator":2}],
+      // seems like a good idea not to use explicit undefined
+      "no-undefined": "error",
+
+      // TODO maybe
+      "camelcase": "off", // TODO: turn on later
+      "init-declarations": ["error","always"]
+    },
+    "overrides": [
+      {
+        "files": ["src/languages/*.js"],
+        "rules": {
+          "no-unused-expressions": "off",
+          // languages are all over the map and we don't want to
+          // do a mass edit so turn off the most egregious rule violations
+          "indent": "off",
+          "comma-dangle": "off",
+          "array-bracket-spacing": "off",
+          "object-curly-spacing": "off",
+          "key-spacing": "off",
+          "object-curly-newline": "off",
+          "object-property-newline": "off"
+        }
+      }
+    ]
+};

.jshintrc

@@ -1,5 +1,7 @@
 // whole codebase isn't ES8/9 yet, but our tests and some things are
 {
     "esversion": 9,
-    "node": true
+    "node": true,
+    // eslint warns us about semicolons
+    "-W033": false
 }