Setup eslint and enforce rules

package.json

@@ -38,10 +38,13 @@
   },
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1",
+    "prebuild": "pnpm run lint",
     "build": "tsc",
     "app": "tsc && node lib/index.js",
     "prepare": "pnpm run build",
-    "docs:build": "typedoc --options typedoc.json"
+    "docs:build": "typedoc --options typedoc.json",
+    "lint": "eslint . --ext .ts",
+    "lint:fix": "eslint --fix . --ext .ts"
   },
   "files": [
     "lib/**/*"
@@ -53,5 +56,10 @@
     "url": "https://code.garrettmills.dev/extollo/lib"
   },
   "author": "garrettmills <shout@garrettmills.dev>",
-  "license": "MIT"
+  "license": "MIT",
+  "devDependencies": {
+    "@typescript-eslint/eslint-plugin": "^4.26.0",
+    "@typescript-eslint/parser": "^4.26.0",
+    "eslint": "^7.27.0"
+  }
 }