Adds (sort) 'options' feature and new tests/docs

[matteocng]

The following commits improve the existing code, docs and tests:

• test/docs: add test and docs for the custom sort function parameter
• test: add non-array/non-object test

This one adds the new feature:

• feat: add 'options' support with a new third, optional parameter

See: #2

[Kikobeats]

Comments ahead. Thanks for that!

Question: Are ignoreArrayAtKeys ignoreObjectAtKeys actually necessary? is not enough using compare method for exclude things that you want?

[matteocng]

@Kikobeats the custom compare function (modified to pass the current 'key' as the third parameter, so that you'd have more control) could get the job done if one was using finepack's API (unless we added support for .js configuration files to bumped - like eslint, postcss - so that not just static values, but functions too could be passed to plugins). When using finepack via bumped-finepack (and a JSON/CSON/YAML .bumpedrc) instead, those parameters (with the related PR that I can contribute to finepack) can let one do something very convenient:

plugins:
  postrelease:
    'Lint config files':
      plugin: 'bumped-finepack'
      opts:
        sortOptions:
          ignoreObjectAtKeys: [
            'rules' 
          ]    

This way users who need the ignore feature don't have to use the API, they just need to add a few lines to their .bumpedrc file.

[Kikobeats]

ok, it has sense, but use compare as options property for avoid pass null 👍