Starting to add eslint CodingTrain#496

This is not at all ready to be merged. I am learning about how linting
works and am starting this branch to sort it out. Some questions:

* I have a `package.json` now in the root directory. Should this be
moved to a `linting` directory or merged with
`unit_testing/package.json`?
* As suggested by @Versatilus I am starting with the p5.js
`.eslintrc.js` configuration. This can change over time.

I'll continue the discussion in the pull request comment thread.

.eslintrc.js

@@ -0,0 +1,61 @@
+module.exports = {
+  env: {
+    browser: true,
+    amd: true,
+    es6: true
+  },
+  extends: ['eslint:recommended', 'prettier'],
+  plugins: ['prettier'],
+  rules: {
+    'prettier/prettier': [
+      'error',
+      {
+        singleQuote: true
+      }
+    ],
+    'no-cond-assign': [2, 'except-parens'],
+    eqeqeq: ['error', 'smart'],
+    'no-use-before-define': [
+      2,
+      {
+        functions: false
+      }
+    ],
+    'new-cap': 0,
+    'no-caller': 2,
+    'no-undef': 2,
+    'no-unused-vars': ['error', {
+      args: 'none'
+    }],
+    'no-empty': ['error', {
+      allowEmptyCatch: true
+    }],
+    'no-console': 'off'
+  }
+};
+
+// module.exports = {
+//   "env": {
+//     "browser": true,
+//     "es6": true
+//   },
+//   "extends": "eslint:recommended",
+//   "rules": {
+//     "indent": [
+//       "error",
+//       4
+//     ],
+//     "linebreak-style": [
+//       "error",
+//       "unix"
+//     ],
+//     "quotes": [
+//       "error",
+//       "single"
+//     ],
+//     "semi": [
+//       "error",
+//       "always"
+//     ]
+//   }
+// };