Split eslintrc files

.eslintrc

@@ -1,13 +1,12 @@
 # https://github.com/eslint/eslint/blob/master/docs/rules/README.md
 
 parserOptions:
-  ecmaVersion: 2017
+  ecmaVersion: 2015
 
 env:
   browser: true
   es6: true
   webextensions: true
-  node: true
 
 globals:
   # messaging.js
@@ -225,7 +224,7 @@ rules:
   no-unsafe-negation: [2]
   no-unused-expressions: [1]
   no-unused-labels: [0]
-  no-unused-vars: [0]
+  no-unused-vars: [1, {args: after-used, vars: local, argsIgnorePattern: ^_}]
   no-use-before-define: [2, nofunc]
   no-useless-call: [2]
   no-useless-computed-key: [2]

tools/.eslintrc

@@ -0,0 +1,9 @@
+# https://github.com/eslint/eslint/blob/master/docs/rules/README.md
+
+parserOptions:
+  ecmaVersion: 2017
+
+env:
+  browser: true
+  es6: true
+  node: true