Add standard-with-typescript linting

Author: zerodevx

.eslintrc.js

@@ -1,15 +1,16 @@
 module.exports = {
   parserOptions: {
     ecmaVersion: 2018,
-    sourceType: 'module'
+    sourceType: 'module',
+    project: './tsconfig.json'
   },
   env: {
     es6: true,
     browser: true,
     node: true
   },
   extends: [
-    'standard'
+    'standard-with-typescript'
   ],
   plugins: [
     'svelte3',

tsconfig.json

@@ -0,0 +1,8 @@
+{
+  "compilerOptions": {
+    "strictNullChecks": true
+  },
+  "files": [
+    "src/index.d.ts"
+  ]
+}