Set up tslint properly

package.json

@@ -5,6 +5,7 @@
   "main": "dist/bundle.js",
   "scripts": {
     "build:core": "node buildCore.js",
+    "lint": "tslint --project tsconfig.json",
     "start": "webpack-dev-server --open",
     "start:electron": "webpack --electron && electron dist/index.html",
     "serve": "webpack-dev-server",

tslint.json

@@ -1,11 +1,17 @@
 {
-    "defaultSeverity": "warning",
+    "defaultSeverity": "error",
     "extends": [
         "tslint:recommended"
     ],
     "jsRules": {
         "object-literal-sort-keys": false
     },
+    "linterOptions": {
+        "exclude": [
+            "src/livesplit-core/**",
+            "src/type-definitions/**"
+        ]
+    },
     "rules": {
         "semicolon": [
             true,
@@ -22,7 +28,6 @@
         "object-literal-sort-keys": [
             false
         ],
-        "strict-boolean-expressions": true,
         "no-invalid-this": [
             true
         ],