chore: configure prettier and eslint

- add prettier to do formatting
- add eslint-config-prettier to
  disable rules conflicting with prettier
- remove eslint from grunt workflow
- use lint-stage to lint and format
  on precommit
- use eslint and prettier in travis directly
- remove rules that are already part of
  the "recommended" ruleset

That rational is that eslint and prettier should be run in
Travis-CI, on commit and as IDE integration (highlighting
errors directlry). They don't need to be run along with
test-cases. Getting linting errors when running the tests
because of missing semicolons is just annoying, but doesn't
help the overall code-quality.

bench/.eslintrc

@@ -1,4 +1,5 @@
 {
+  "extends": "prettier",
   "globals": {
     "require": true
   },
@@ -11,4 +12,4 @@
     "handle-callback-err": 0,
     "no-console": 0
   }
-}
+}