Add eslint and prettier.

package.json

@@ -6,7 +6,8 @@
   "main": "lib/main.js",
   "scripts": {
     "build": "tsc",
-    "test": "jest"
+    "test": "tsc --noEmit && jest",
+    "lint": "eslint . --ext .ts"
   },
   "repository": {
     "type": "git",
@@ -27,8 +28,15 @@
   "devDependencies": {
     "@types/jest": "^24.0.13",
     "@types/node": "^12.0.4",
+    "@typescript-eslint/eslint-plugin": "^2.6.1",
+    "@typescript-eslint/parser": "^2.6.1",
+    "eslint": "^6.6.0",
+    "eslint-config-prettier": "^6.5.0",
+    "eslint-plugin-import": "^2.18.2",
+    "eslint-plugin-prettier": "^3.1.1",
     "jest": "^24.8.0",
     "jest-circus": "^24.7.1",
+    "prettier": "^1.18.2",
     "ts-jest": "^24.0.2",
     "typescript": "^3.5.1"
   }