Feature Request: ignore rules per file

[roaldnefs]

Preface

As @myii suggests on Slack, it would be useful to have to option to ignore rules per file:

Having the ability to ignore rules per file would be really useful. We're using that with yamllint.

So here's a sample configuration:

---
# Extend the `default` configuration provided by `yamllint`
extends: default

# Files to ignore completely
# 1. All YAML files under directory `node_modules/`, introduced during the Travis run
# 2. Any SLS files under directory `test/`, which are actually state files
# 3. Any YAML files under directory `.kitchen/`, introduced during local testing
ignore: |
  node_modules/
  test/**/states/**/*.sls
  .kitchen/

rules:
  commas:
    # Allow separation between commas to achieve tabular layout under `platforms`
    ignore: |
      ssf/defaults.yaml
      ssf/formulas.yaml

Description

Add to option to ignore rules per file (using the .salt-lint configuration file) like yamllint is doing.

[myii]

@roaldnefs If the yamllint format doesn't suit you, have a look at how Flake8 does it as well.