Config file support

[alexis-exaud]

Instead of having to run sync-i18n --files '**/locales/*.json' --primary en --languages es fr ja zh ko --space 2

It would be nice to be able to run sync-i18n i18next-json-sync.config.js

Where i18next-json-sync.config.js would be:

module.exports = {
  files: '**/locales/*.json',
  primary: 'en',
  createResources: ["en", "fr", "ja", "zh", "ko"],
  space: 2
}